diff --git a/Core/Src/Gui/app_gui.h b/Core/Src/Gui/app_gui.h
index e3a68a2..5f71a7a 100644
--- a/Core/Src/Gui/app_gui.h
+++ b/Core/Src/Gui/app_gui.h
@@ -41,6 +41,7 @@ uint32_t push_time();
 void screen_home(GuiEvent event);
 void screen_manual(GuiEvent event);
 void screen_manual_menu(GuiEvent event);
+void screen_calibration(GuiEvent event);
 
 struct State {
     /// Latest oven temp readout
@@ -78,24 +79,6 @@ struct State {
 
     /// Pointer to the currently active screen func
     screen_t screen;
-
-    /// Generic menu
-    struct menu_state {
-        int pos;
-        int len;
-        uint32_t change_time;
-        uint32_t slide_end_time;
-        uint16_t text_slide;
-        uint8_t tick_counter;
-    } menu;
-
-    struct calib_state {
-        int phase;
-        float sample1;
-        float sample2;
-        int temp1;
-        int temp2;
-    } calib;
 };
 
 extern struct State s_app;
diff --git a/Core/Src/Gui/screen_calibration.c b/Core/Src/Gui/screen_calibration.c
index 4b2d22c..64c90c1 100644
--- a/Core/Src/Gui/screen_calibration.c
+++ b/Core/Src/Gui/screen_calibration.c
@@ -4,6 +4,7 @@
 
 
 #include <stddef.h>
+#include <string.h>
 #include "app_gui.h"
 #include "app_heater.h"
 #include "screen_menu.h"
@@ -12,6 +13,28 @@
 #include "snprintf.h"
 #include "FreeRTOS.h"
 
+struct calib_state {
+    int phase;
+    float sample1;
+    float sample2;
+    int temp1;
+    int temp2;
+} s_calib;
+
+enum Phase {
+    PH_HELLO = 0,
+    PH_SAMPLE1,
+    PH_TEMP1,
+    PH_SAMPLE2,
+    PH_TEMP2,
+    PH_DONE,
+};
+
+static void next_phase() {
+    PUTS("Phase++\r\n");
+    s_calib.phase++;
+}
+
 static const char* calib0_opts[] = {
         "Pokračovat",
         "Zrušit",
@@ -22,7 +45,7 @@ static void calib0_cb(int opt) {
     switch (opt) {
         case 0:
             // Continue
-            s_app.calib.phase++;
+            next_phase();
             request_paint();
             app_heater_manual_override(100);
             break;
@@ -41,13 +64,15 @@ static const char* calib1_opts[] = {
 };
 
 
+
+
 static void calib1_cb(int opt) {
     switch (opt) {
         case 0:
             // Continue
-            s_app.calib.phase++;
+            next_phase();
             request_paint();
-            s_app.calib.sample1 = app_temp_read_oven_raw();
+            s_calib.sample1 = app_temp_read_oven_raw();
             app_heater_manual_override(0);
             break;
 
@@ -69,9 +94,9 @@ static void calib3_cb(int opt) {
     switch (opt) {
         case 0:
             // Continue
-            s_app.calib.phase++;
+            next_phase();
             request_paint();
-            s_app.calib.sample2 = app_temp_read_oven_raw();
+            s_calib.sample2 = app_temp_read_oven_raw();
             app_heater_manual_override(0);
             break;
 
@@ -82,54 +107,41 @@ static void calib3_cb(int opt) {
     }
 }
 
-void screen_manual_menu(GuiEvent event)
+void screen_calibration(GuiEvent event)
 {
     if (event == GUI_EVENT_SCREEN_INIT) {
-        s_app.calib.phase = 0;
-        s_app.calib.sample1 = s_app.calib.sample2 = 0.0f;
-        s_app.calib.temp1 = s_app.calib.temp2 = 0;
+        memset(&s_calib, 0, sizeof(s_calib));
+        // continue to the rest - so the menu can be inited
     }
 
-    int phase = s_app.calib.phase;
     int *pT;
-    switch (phase) {
-        case 0:
+    switch (s_calib.phase) {
+        case PH_HELLO:
             if (event == GUI_EVENT_PAINT) {
-                fb_text(FBW/2, 14, "Vychlaďte", TEXT_CENTER, 1);
+                fb_text(FBW/2, 14, "Vychlaď", TEXT_CENTER, 1);
                 fb_text(FBW/2, 24, "troubu", TEXT_CENTER, 1);
             }
-            screen_menu(event, calib1_opts, calib1_cb);
+            screen_menu(event, calib0_opts, calib0_cb);
             break;
 
-        case 1: // Heater is active, waiting for mark
-        case 3:
+        case PH_SAMPLE1: // Heater is active, waiting for mark
+        case PH_SAMPLE2:
             if (event == GUI_EVENT_PAINT) {
                 fb_text(FBW/2, 14, "Zapiš teplotu", TEXT_CENTER, 1);
             }
-            if (phase == 1) {
+            if (s_calib.phase == PH_SAMPLE1) {
                 screen_menu(event, calib1_opts, calib1_cb);
             } else {
                 screen_menu(event, calib3_opts, calib3_cb);
             }
             break;
 
-        case 2:
-        case 4:
-            if (phase == 2) {
-                pT = &s_app.calib.temp1;
+        case PH_TEMP1:
+        case PH_TEMP2:
+            if (s_calib.phase == PH_TEMP1) {
+                pT = &s_calib.temp1;
             } else {
-                pT = &s_app.calib.temp2;
-            }
-
-            if (event == GUI_EVENT_PAINT) {
-                fb_text(FBW/2, 14, phase == 2 ? "Teplota 1" : "Teplota 2", TEXT_CENTER, 1);
-                SPRINTF(stmp, "%d°C", *pT);
-                fb_text(FBW/2, 30, stmp, TEXT_CENTER | FONT_DOUBLE, 1);
-
-                fb_text(2, FBH - 8 * 3, "←→Nastav", 0, 1);
-                fb_text(2, FBH - 8 * 2, "> Potvrdit", 0, 1);
-                fb_text(2, FBH - 8 * 1, "» Zrušit", 0, 1);
-                return;
+                pT = &s_calib.temp2;
             }
 
             if (push_time() > pdMS_TO_TICKS(500)) {
@@ -139,40 +151,62 @@ void screen_manual_menu(GuiEvent event)
                 return;
             }
 
-            if (event == GUI_EVENT_KNOB_PLUS) {
-                if (*pT < 500) {
-                    *pT += 1;
-                    input_sound_effect();
-                    request_paint();
+            switch (event) {
+                case GUI_EVENT_PAINT: {
+                    fb_text(FBW/2, 14, s_calib.phase == PH_TEMP1 ? "Teplota 1" : "Teplota 2", TEXT_CENTER, 1);
+                    SPRINTF(stmp, "%d°C", *pT);
+                    fb_text(FBW/2, 30, stmp, TEXT_CENTER | FONT_DOUBLE, 1);
+
+                    fb_text(2, FBH - 8 * 3, "←→Nastav", 0, 1);
+                    fb_text(2, FBH - 8 * 2, "> Potvrdit", 0, 1);
+                    fb_text(2, FBH - 8 * 1, "» Zrušit", 0, 1);
+                    return;
                 }
-            }
-            else if (event == GUI_EVENT_KNOB_MINUS) {
-                if (*pT > 0) {
-                    input_sound_effect();
-                    *pT -= 1;
-                    request_paint();
+
+                case GUI_EVENT_KNOB_PLUS: {
+                    if (*pT < 500) {
+                        *pT += 1;
+                        input_sound_effect();
+                        request_paint();
+                    }
+                    break;
                 }
-            } else if (event == GUI_EVENT_KNOB_RELEASE) {
-                s_app.calib.phase++;
-                request_paint();
 
-                if (s_app.calib.phase == 5) {
-                    // TODO do the math
-                    PRINTF("Sample 1 %f, T1 %d\r\n", s_app.calib.sample1, s_app.calib.temp1);
-                    PRINTF("Sample 2 %f, T2 %d\r\n", s_app.calib.sample2, s_app.calib.temp2);
+                case GUI_EVENT_KNOB_MINUS: {
+                    if (*pT > 0) {
+                        input_sound_effect();
+                        *pT -= 1;
+                        request_paint();
+                    }
+                    break;
+                }
+
+                case GUI_EVENT_KNOB_RELEASE: {
+                    next_phase();
+                    request_paint();
 
-                    float corrected1 = c_to_val((float) s_app.calib.temp1);
-                    float corrected2 = c_to_val((float) s_app.calib.temp2);
+                    if (s_calib.phase == PH_DONE) {
+                        app_heater_manual_override(-1);
+                        // TODO do the math
+                        PRINTF("Sample 1 %f, T1 %d\r\n", s_calib.sample1, s_calib.temp1);
+                        PRINTF("Sample 2 %f, T2 %d\r\n", s_calib.sample2, s_calib.temp2);
 
-                    float a = ;
-                    float b = ;
+                        float corrected1 = c_to_val((float) s_calib.temp1);
+                        float corrected2 = c_to_val((float) s_calib.temp2);
 
-                    // TODO set and persist calibration
+                        float a = (corrected1 - corrected2) / (s_calib.sample1 - s_calib.sample2);
+                        float b = corrected1 - a * s_calib.sample1;
+
+                        app_temp_set_calib(a, b);
+                    } else {
+                        app_heater_manual_override(100);
+                    }
+                    break;
                 }
             }
             break;
 
-        case 5:
+        case PH_DONE:
             if (event == GUI_EVENT_PAINT) {
                 fb_text(FBW/2, 14, "Hotovo", TEXT_CENTER, 1);
                 fb_text(FBW/2, 36, "→Hlavní menu", TEXT_CENTER, 1);
@@ -182,5 +216,4 @@ void screen_manual_menu(GuiEvent event)
             }
             break;
     }
-
 }
diff --git a/Core/Src/Gui/screen_home.c b/Core/Src/Gui/screen_home.c
index 6acf398..f4b5c2f 100644
--- a/Core/Src/Gui/screen_home.c
+++ b/Core/Src/Gui/screen_home.c
@@ -12,8 +12,8 @@
 static const char* main_menu_opts[] = {
         "Ruční režim",
         "Kalibrace",
-        "Programy",
-        "Diagnostika",
+//        "Programy",
+//        "Diagnostika",
         NULL
 };
 
@@ -23,7 +23,7 @@ static void main_menu_cb(int opt) {
             switch_screen(screen_manual, true);
             break;
         case 1:
-            // TODO
+            switch_screen(screen_calibration, true);
             break;
     }
 }
diff --git a/Core/Src/Gui/screen_menu.c b/Core/Src/Gui/screen_menu.c
index 87d6afa..d92e312 100644
--- a/Core/Src/Gui/screen_menu.c
+++ b/Core/Src/Gui/screen_menu.c
@@ -3,6 +3,7 @@
 //
 
 #include <stdbool.h>
+#include <string.h>
 #include "screen_menu.h"
 #include "app_gui.h"
 #include "FreeRTOS.h"
@@ -12,40 +13,53 @@
 #include "ufb/framebuffer.h"
 #include "ufb/fb_text.h"
 
+struct menu_state {
+    int pos;
+    int len;
+    uint32_t change_time;
+    uint32_t slide_end_time;
+    uint16_t text_slide;
+    void * last_opts;
+} s_menu;
 
 void screen_menu(GuiEvent event, const char **options, menu_callback_t cb) {
+    if (event != GUI_EVENT_SCREEN_INIT && s_menu.last_opts != (void*) options) {
+        // ensure the menu is properly inited when the options list changes.
+        screen_menu(GUI_EVENT_SCREEN_INIT, options, cb);
+    }
+
     bool menu_changed = false;
     const uint32_t tickNow = xTaskGetTickCount();
 
-    struct menu_state *menu = &s_app.menu;
-
     switch (event) {
         case GUI_EVENT_SCREEN_INIT:
-            menu->pos = 0;
-            menu->len = 0;
-            menu->change_time = tickNow;
-            menu->text_slide = 0;
+            memset(&s_menu, 0, sizeof(s_menu));
+            s_menu.last_opts = (void*) options;
+
+            s_menu.change_time = tickNow;
+
+            // count options
             const char **opt = options;
             while (*opt) {
-                menu->len++;
+                s_menu.len++;
                 opt++;
             }
             break;
 
         case GUI_EVENT_SCREEN_TICK:
             // long text sliding animation
-            if (tickNow - menu->change_time >= pdMS_TO_TICKS(500)) {
-                const uint32_t textlen = utf8_strlen(options[menu->pos]) * 6;
+            if (tickNow - s_menu.change_time >= pdMS_TO_TICKS(500)) {
+                const uint32_t textlen = utf8_strlen(options[s_menu.pos]) * 6;
                 if (textlen >= FBW - 2) {
-                    if (textlen - menu->text_slide > FBW - 1) {
-                        menu->text_slide += 1;
-                        if (textlen - menu->text_slide >= FBW - 1) {
-                            menu->slide_end_time = tickNow;
+                    if (textlen - s_menu.text_slide > FBW - 1) {
+                        s_menu.text_slide += 1;
+                        if (textlen - s_menu.text_slide >= FBW - 1) {
+                            s_menu.slide_end_time = tickNow;
                         }
-                    } else if (tickNow - menu->slide_end_time >= pdMS_TO_TICKS(500)) {
-                        menu->change_time = tickNow;
-                        menu->slide_end_time = 0;
-                        menu->text_slide = 0;
+                    } else if (tickNow - s_menu.slide_end_time >= pdMS_TO_TICKS(500)) {
+                        s_menu.change_time = tickNow;
+                        s_menu.slide_end_time = 0;
+                        s_menu.text_slide = 0;
                     }
                     request_paint();
                 }
@@ -53,13 +67,13 @@ void screen_menu(GuiEvent event, const char **options, menu_callback_t cb) {
             break;
 
         case GUI_EVENT_PAINT:
-            for (int i = 0; i < menu->len; i++) {
+            for (int i = 0; i < s_menu.len; i++) {
                 // is the row currently rendered the selected row?
-                const bool is_selected = menu->pos == i;
+                const bool is_selected = s_menu.pos == i;
                 const fbcolor_t color = !is_selected; // text color - black if selected, because it's inverted
                 const fbpos_t y = 27 + i * 10;
                 fb_rect(0, y, FBW, 10, !color);
-                fb_text(1 - (is_selected ? menu->text_slide : 0), y + 1, options[i], FONT_5X7, color);
+                fb_text(1 - (is_selected ? s_menu.text_slide : 0), y + 1, options[i], FONT_5X7, color);
                 // ensure the text doesn't touch the edge (looks ugly)
                 fb_vline(FBW - 1, y, 10, !color);
                 fb_vline(0, y, 10, !color);
@@ -69,28 +83,28 @@ void screen_menu(GuiEvent event, const char **options, menu_callback_t cb) {
             // the button is held! release is what activates the button
         case GUI_EVENT_KNOB_RELEASE:
             input_sound_effect();
-            cb(menu->pos);
+            cb(s_menu.pos);
             break;
 
         case GUI_EVENT_KNOB_PLUS:
-            if (menu->pos < menu->len - 1) {
-                menu->pos++;
+            if (s_menu.pos < s_menu.len - 1) {
+                s_menu.pos++;
                 menu_changed = true;
             }
             break;
 
         case GUI_EVENT_KNOB_MINUS:
-            if (menu->pos > 0) {
-                menu->pos--;
+            if (s_menu.pos > 0) {
+                s_menu.pos--;
                 menu_changed = true;
             }
             break;
     }
 
     if (menu_changed) {
-        menu->change_time = tickNow;
-        menu->text_slide = 0;
-        menu->slide_end_time = 0;
+        s_menu.change_time = tickNow;
+        s_menu.text_slide = 0;
+        s_menu.slide_end_time = 0;
         input_sound_effect();
         request_paint();
     }
diff --git a/Core/Src/app_heater.c b/Core/Src/app_heater.c
index 9d15a03..9449330 100644
--- a/Core/Src/app_heater.c
+++ b/Core/Src/app_heater.c
@@ -66,6 +66,8 @@ static inline void heaterExitCritical() {
 }
 
 void app_heater_manual_override(int percent) {
+    PRINTF("Set manual override: %d\r\n", percent);
+
     heaterEnterCritical();
     PID_SetCtlMode(&state.pid, PID_MANUAL);
     state.manual_override = percent;
diff --git a/Core/Src/app_temp.c b/Core/Src/app_temp.c
index fbd0b9f..0f5aebc 100644
--- a/Core/Src/app_temp.c
+++ b/Core/Src/app_temp.c
@@ -26,17 +26,17 @@ const float V_REFINT = 1.23f;
 
 static struct App {
   float oven_temp;
+  float oven_temp_raw;
   float soc_temp;
-  float v_sensor;
   float cal_a;
   float cal_b;
+  float oventemp_history[OVENTEMP_HISTORY_DEPTH]; // raw temp
   uint16_t adc_averagebuf[AVERAGEBUF_DEPTH * 4];
   uint8_t averagebuf_ptr;
-  float adc_averages[4];
-  float oventemp_history[OVENTEMP_HISTORY_DEPTH];
   uint8_t oventemp_history_ptr;
 } s_analog = {
-        .cal_a = 1.0f,
+        // Ax + B = y ... X = raw sample (ratio 0-1 of 3.3), Y = corrected sample
+        .cal_a = 1.0f, // safe default calibration constants
         .cal_b = 0.0f,
 };
 
@@ -148,6 +148,35 @@ static const float TSENSE_LOOKUP[TSENSE_LOOKUP_LEN] = {
         0.219346163379138f,
 };
 
+/// if the calibration constants are zero, reset to defaults
+static void correct_invalid_calib() {
+    if (s_analog.cal_a == 0.0f || s_analog.cal_b == 0.0f) {
+        PRINTF("ADC invalid calib, reset\r\n");
+        s_analog.cal_a = 1.0f;
+        s_analog.cal_b = 0.0f;
+    }
+}
+
+/// Set and persist calibration constants
+void app_temp_set_calib(float a, float b) {
+    s_analog.cal_a = a;
+    s_analog.cal_b = b;
+    correct_invalid_calib();
+
+    EE_Status st = EE_WriteVariable32bits(EE_ADDR_CAL_A, ((x32_t) { .f = a }).u);
+    if (st == EE_CLEANUP_REQUIRED) {
+        EE_CleanUp();
+    } else if (st != EE_OK) {
+        PRINTF("EE write err %d!\r\n", st);
+    }
+    st = EE_WriteVariable32bits(EE_ADDR_CAL_B, ((x32_t) { .f = b }).u);
+    if (st == EE_CLEANUP_REQUIRED) {
+        EE_CleanUp();
+    } else if (st != EE_OK) {
+        PRINTF("EE write err %d!\r\n", st);
+    }
+}
+
 void app_analog_init()
 {
     // read calibration constants
@@ -161,11 +190,7 @@ void app_analog_init()
         PRINTF("ADC calib b read from EE: %f\r\n", s_analog.cal_b);
     }
 
-    if (s_analog.cal_a == 0.0f || s_analog.cal_b == 0.0f) {
-        PRINTF("ADC invalid calib, reset\r\n");
-        s_analog.cal_a = 1.0f;
-        s_analog.cal_b = 0.0f;
-    }
+    correct_invalid_calib();
 
     LL_ADC_Enable(ADC_TEMP);
 
@@ -192,7 +217,7 @@ void app_analog_init()
     LL_TIM_EnableCounter(TIM1);
 }
 
-static float val_to_c(float val)
+float val_to_c(float val)
 {
     // TODO use binary search.. lol
     for (int i = 1; i < TSENSE_LOOKUP_LEN; i++) {
@@ -207,6 +232,22 @@ static float val_to_c(float val)
     return TSENSE_T_MAX;
 }
 
+float c_to_val(float cf)
+{
+    int lower = (int) (cf / TSENSE_T_STEP);
+
+    if (lower < 0) {
+        lower = 0;
+    }
+    if (lower >= TSENSE_LOOKUP_LEN - 1) {
+        lower = TSENSE_LOOKUP_LEN - 2;
+    }
+    int upper = lower + 1;
+
+    float ratio = (cf - ((float)lower * TSENSE_T_STEP)) / 5.0f;
+    return TSENSE_LOOKUP[lower] + (TSENSE_LOOKUP[upper] - TSENSE_LOOKUP[lower]) * ratio;
+}
+
 void app_temp_sample()
 {
     uint32_t sums[4] = {};
@@ -224,39 +265,38 @@ void app_temp_sample()
         return;
     }
 
-    s_analog.adc_averages[0] = (float) sums[0] / count;
-    s_analog.adc_averages[1] = (float) sums[1] / count;
-    s_analog.adc_averages[2] = (float) sums[2] / count;
-    s_analog.adc_averages[3] = (float) sums[3] / count;
+    float adc_averages[4];
+
+    adc_averages[0] = (float) sums[0] / count;
+    adc_averages[1] = (float) sums[1] / count;
+    adc_averages[2] = (float) sums[2] / count;
+    adc_averages[3] = (float) sums[3] / count;
 
     PRINTF("%f\t%f\t%f\t%f\r\n",
-           s_analog.adc_averages[0],
-                   s_analog.adc_averages[1],
-                   s_analog.adc_averages[2],
-                   s_analog.adc_averages[3]
+           adc_averages[0],
+                   adc_averages[1],
+                   adc_averages[2],
+                   adc_averages[3]
            );
 
     /* r_pt100, r_ref, internal_temp, v_ref_int */
-    float refint = s_analog.adc_averages[3];
+    float refint = adc_averages[3];
     float scale = V_REFINT / refint;
 
     const float avg_slope = 4.3f * scale;
     const float v25 = 1.43f;
-    const float v_tsen = s_analog.adc_averages[2] * scale;
+    const float v_tsen = adc_averages[2] * scale;
 
     s_analog.soc_temp = (v25 - v_tsen) / avg_slope + 25.f;
-    s_analog.v_sensor = s_analog.adc_averages[0] * scale; // good for debug/tuning
+    //s_analog.v_sensor = adc_averages[0] * scale; // good for debug/tuning
 
 
     // using a voltage divider, so assuming the reference resistor is measured well,
     // we can just use the ratio and the exact voltage value is not important.
 
-    float x = s_analog.adc_averages[0] / s_analog.adc_averages[1];
-    float y = s_analog.cal_a * x + s_analog.cal_b;
-    float actual_temp = val_to_c(y);
-    PRINTF("Compensated x %f -> y %f, temp %f C\r\n", x, y, actual_temp);
+    float oventemp_sample = adc_averages[0] / adc_averages[1];
 
-    s_analog.oventemp_history[s_analog.oventemp_history_ptr] = actual_temp;
+    s_analog.oventemp_history[s_analog.oventemp_history_ptr] = oventemp_sample;
     s_analog.oventemp_history_ptr = (s_analog.oventemp_history_ptr + 1) % OVENTEMP_HISTORY_DEPTH;
 
     float sum = 0;
@@ -270,15 +310,21 @@ void app_temp_sample()
     if (depth > 0) {
         sum /= depth;
     }
-    s_analog.oven_temp = sum;
+
+    float y = s_analog.cal_a * sum + s_analog.cal_b;
+    float actual_temp = val_to_c(y);
+    PRINTF("Compensated x %f -> y %f, temp %f C\r\n", sum, y, actual_temp);
+
+    s_analog.oven_temp = actual_temp;
+    s_analog.oven_temp_raw = sum;
 
     app_safety_pass_temp_calculation();
 
-    if (s_analog.oven_temp >= 5.0 && s_analog.oven_temp <= 455.0) {
+    if (s_analog.oven_temp_raw >= 0.05 && s_analog.oven_temp_raw <= 0.22) {
         app_safety_pass_temp_normal();
     }
 
-    if (s_analog.soc_temp >= 5.0 && s_analog.soc_temp <= 80.0) {
+    if (s_analog.soc_temp >= 2.0 && s_analog.soc_temp <= 80.0) {
         app_safety_pass_soc_temp_ok();
     }
 }
@@ -288,6 +334,11 @@ float app_temp_read_oven()
     return s_analog.oven_temp;
 }
 
+float app_temp_read_oven_raw()
+{
+    return s_analog.oven_temp_raw;
+}
+
 float app_temp_read_soc()
 {
     return s_analog.soc_temp;
diff --git a/Core/Src/app_temp.h b/Core/Src/app_temp.h
index b74e943..85425ee 100644
--- a/Core/Src/app_temp.h
+++ b/Core/Src/app_temp.h
@@ -7,6 +7,11 @@
 
 void app_analog_init();
 
+float val_to_c(float val);
+float c_to_val(float c);
+
+void app_temp_set_calib(float a, float b);
+
 /**
  * Update temperature measurement.
  *