diff --git a/Core/Src/Gui/app_gui.c b/Core/Src/Gui/app_gui.c
index 849f222..d4af5c7 100644
--- a/Core/Src/Gui/app_gui.c
+++ b/Core/Src/Gui/app_gui.c
@@ -124,7 +124,6 @@ void switch_screen(screen_t pScreen, bool init) {
     s_app.initial_pushed = s_app.pushed;
     s_app.screen = pScreen;
     // clear the union field
-    memset(&s_app.page, 0, sizeof(s_app.page));
     request_paint();
 
     if (init) {
diff --git a/Core/Src/Gui/app_gui.h b/Core/Src/Gui/app_gui.h
index fd03144..e3a68a2 100644
--- a/Core/Src/Gui/app_gui.h
+++ b/Core/Src/Gui/app_gui.h
@@ -79,18 +79,23 @@ struct State {
     /// Pointer to the currently active screen func
     screen_t screen;
 
-    /// data specific for each of the screens (not persistent across screen switching)
-    union {
-        /// 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;
-    } page;
+    /// 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
new file mode 100644
index 0000000..4b2d22c
--- /dev/null
+++ b/Core/Src/Gui/screen_calibration.c
@@ -0,0 +1,186 @@
+//
+// Created by MightyPork on 2023/04/09.
+//
+
+
+#include <stddef.h>
+#include "app_gui.h"
+#include "app_heater.h"
+#include "screen_menu.h"
+#include "ufb/fb_text.h"
+#include "app_temp.h"
+#include "snprintf.h"
+#include "FreeRTOS.h"
+
+static const char* calib0_opts[] = {
+        "Pokračovat",
+        "Zrušit",
+        NULL
+};
+
+static void calib0_cb(int opt) {
+    switch (opt) {
+        case 0:
+            // Continue
+            s_app.calib.phase++;
+            request_paint();
+            app_heater_manual_override(100);
+            break;
+
+        case 1:
+            switch_screen(screen_home, true);
+            break;
+    }
+}
+
+
+static const char* calib1_opts[] = {
+        "Vzorek 1",
+        "Zrušit",
+        NULL
+};
+
+
+static void calib1_cb(int opt) {
+    switch (opt) {
+        case 0:
+            // Continue
+            s_app.calib.phase++;
+            request_paint();
+            s_app.calib.sample1 = app_temp_read_oven_raw();
+            app_heater_manual_override(0);
+            break;
+
+        case 1:
+            app_heater_manual_override(-1);
+            switch_screen(screen_home, true);
+            break;
+    }
+}
+
+static const char* calib3_opts[] = {
+        "Vzorek 2",
+        "Zrušit",
+        NULL
+};
+
+
+static void calib3_cb(int opt) {
+    switch (opt) {
+        case 0:
+            // Continue
+            s_app.calib.phase++;
+            request_paint();
+            s_app.calib.sample2 = app_temp_read_oven_raw();
+            app_heater_manual_override(0);
+            break;
+
+        case 1:
+            app_heater_manual_override(-1);
+            switch_screen(screen_home, true);
+            break;
+    }
+}
+
+void screen_manual_menu(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;
+    }
+
+    int phase = s_app.calib.phase;
+    int *pT;
+    switch (phase) {
+        case 0:
+            if (event == GUI_EVENT_PAINT) {
+                fb_text(FBW/2, 14, "Vychlaďte", TEXT_CENTER, 1);
+                fb_text(FBW/2, 24, "troubu", TEXT_CENTER, 1);
+            }
+            screen_menu(event, calib1_opts, calib1_cb);
+            break;
+
+        case 1: // Heater is active, waiting for mark
+        case 3:
+            if (event == GUI_EVENT_PAINT) {
+                fb_text(FBW/2, 14, "Zapiš teplotu", TEXT_CENTER, 1);
+            }
+            if (phase == 1) {
+                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;
+            } 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;
+            }
+
+            if (push_time() > pdMS_TO_TICKS(500)) {
+                input_sound_effect();
+                app_heater_manual_override_clear();
+                switch_screen(screen_home, true);
+                return;
+            }
+
+            if (event == GUI_EVENT_KNOB_PLUS) {
+                if (*pT < 500) {
+                    *pT += 1;
+                    input_sound_effect();
+                    request_paint();
+                }
+            }
+            else if (event == GUI_EVENT_KNOB_MINUS) {
+                if (*pT > 0) {
+                    input_sound_effect();
+                    *pT -= 1;
+                    request_paint();
+                }
+            } 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);
+
+                    float corrected1 = c_to_val((float) s_app.calib.temp1);
+                    float corrected2 = c_to_val((float) s_app.calib.temp2);
+
+                    float a = ;
+                    float b = ;
+
+                    // TODO set and persist calibration
+                }
+            }
+            break;
+
+        case 5:
+            if (event == GUI_EVENT_PAINT) {
+                fb_text(FBW/2, 14, "Hotovo", TEXT_CENTER, 1);
+                fb_text(FBW/2, 36, "→Hlavní menu", TEXT_CENTER, 1);
+            }
+            if (event == GUI_EVENT_KNOB_RELEASE) {
+                switch_screen(screen_home, 1);
+            }
+            break;
+    }
+
+}
diff --git a/Core/Src/Gui/screen_manual.c b/Core/Src/Gui/screen_manual.c
index e0e35e5..268b9fb 100644
--- a/Core/Src/Gui/screen_manual.c
+++ b/Core/Src/Gui/screen_manual.c
@@ -17,6 +17,8 @@ void screen_manual(GuiEvent event)
 {
     bool temp_changed = false;
     if (event == GUI_EVENT_SCREEN_INIT) {
+        app_heater_manual_override_clear();
+        app_heater_enable(false);
         return;
     }
 
diff --git a/Core/Src/Gui/screen_menu.c b/Core/Src/Gui/screen_menu.c
index 8b89b78..87d6afa 100644
--- a/Core/Src/Gui/screen_menu.c
+++ b/Core/Src/Gui/screen_menu.c
@@ -17,7 +17,7 @@ void screen_menu(GuiEvent event, const char **options, menu_callback_t cb) {
     bool menu_changed = false;
     const uint32_t tickNow = xTaskGetTickCount();
 
-    struct menu_state *menu = &s_app.page.menu;
+    struct menu_state *menu = &s_app.menu;
 
     switch (event) {
         case GUI_EVENT_SCREEN_INIT:
diff --git a/Core/Src/app_heater.c b/Core/Src/app_heater.c
index cf90b07..9d15a03 100644
--- a/Core/Src/app_heater.c
+++ b/Core/Src/app_heater.c
@@ -39,12 +39,15 @@ static struct {
   float tuning_p;
   float tuning_i;
   float tuning_d;
+  /// Manual PWM override (percent, -1 = override disable)
+  int manual_override;
   // PID state
   struct PID pid;
 } state = {
         .tuning_p = 10.0f,
         .tuning_i = 0.052f,
         .tuning_d = 100.0f,
+        .manual_override = -1,
         .pid = {
                 .SampleTimeTicks = pdMS_TO_TICKS(1000),
                 .outMax = 100.0f,
@@ -62,6 +65,17 @@ static inline void heaterExitCritical() {
     osMutexRelease(heaterMutexHandle);
 }
 
+void app_heater_manual_override(int percent) {
+    heaterEnterCritical();
+    PID_SetCtlMode(&state.pid, PID_MANUAL);
+    state.manual_override = percent;
+    heaterExitCritical();
+}
+
+void app_heater_manual_override_clear() {
+    app_heater_manual_override(-1);
+}
+
 void app_heater_set_tuning(float p, float i, float d) {
     heaterEnterCritical();
     PID_SetTunings(&state.pid, p, i, d);
@@ -127,13 +141,19 @@ void app_task_heater(void *argument)
 
         heaterEnterCritical();
         app_safety_pass_reg_loop_running();
-        PID_Compute(&state.pid, state.oven_temp);
-        if (state.pid.ctlMode == PID_AUTOMATIC) {
-            PRINTF("temp %d, output %d\r\n", (int) state.oven_temp, (int) state.pid.Output);
+
+        if (state.manual_override >= 0 && state.manual_override <= 100) {
+            PRINTF("manual override %d%%\r\n", state.manual_override);
             heater_pwm_set_perc(state.pid.Output);
         } else {
-            // turn it off
-            heater_pwm_set_perc(0);
+            PID_Compute(&state.pid, state.oven_temp);
+            if (state.pid.ctlMode == PID_AUTOMATIC) {
+                PRINTF("temp %d, output %d\r\n", (int) state.oven_temp, (int) state.pid.Output);
+                heater_pwm_set_perc(state.pid.Output);
+            } else {
+                // turn it off
+                heater_pwm_set_perc(0);
+            }
         }
         heaterExitCritical();
 
diff --git a/Core/Src/app_heater.h b/Core/Src/app_heater.h
index e264ba7..edcc9ba 100644
--- a/Core/Src/app_heater.h
+++ b/Core/Src/app_heater.h
@@ -14,6 +14,13 @@ extern osThreadId_t heaterTskHandle;
 
 void app_task_heater(void *argument);
 
+/// Clear manual override, disable heater for normal mode.
+void app_heater_manual_override_clear();
+
+/// Set manual override PWM 0-100%.
+/// Also disables heater in the normal mode.
+void app_heater_manual_override(int percent);
+
 /// Set heater regulator tuning.
 /// Mutex is locked internally.
 void app_heater_set_tuning(float p, float i, float d);
diff --git a/Core/Src/app_temp.h b/Core/Src/app_temp.h
index 6972ba4..b74e943 100644
--- a/Core/Src/app_temp.h
+++ b/Core/Src/app_temp.h
@@ -20,6 +20,9 @@ void app_temp_sample();
 /// The value is valid after calling app_temp_sample()
 float app_temp_read_oven();
 
+/// Get the raw ADC value (divider voltage)
+float app_temp_read_oven_raw();
+
 /// Read current SOC temperature (celsius)
 /// The value is valid after calling app_temp_sample()
 float app_temp_read_soc();
diff --git a/Makefile b/Makefile
index dd2ad3c..9bac69c 100644
--- a/Makefile
+++ b/Makefile
@@ -51,6 +51,7 @@ Core/Src/Gui/app_gui.c \
 Core/Src/Gui/screen_menu.c \
 Core/Src/Gui/screen_home.c \
 Core/Src/Gui/screen_manual.c \
+Core/Src/Gui/screen_calibration.c \
 Core/Src/Gui/screen_manual_menu.c \
 Core/Src/app_temp.c \
 Core/Src/app_knob.c \