diff --git a/firmware/src/customize.cpp b/firmware/src/customize.cpp
index ce24a82..6ca841f 100644
--- a/firmware/src/customize.cpp
+++ b/firmware/src/customize.cpp
@@ -4,18 +4,52 @@
 
 void customize_setup();
 
-void customize() {
-  while (true) {
-    customize_setup();
-    float wireDiameter = number_input(-1, 0.1);
-    tick();
-    Serial.println(wireDiameter);
-  }
-}
+float wireDiameter = -1;
+float coreLength = -1;
 
-void customize_setup() {
+void customize() {
+setup:
+  wireDiameter = -1;
+  coreLength = -1;
+
+wireDiameterStep:
   lcd.clear();
   lcd.print("Wire diameter:");
   lcd.setCursor(14, 1);
   lcd.print("mm");
+
+  float inputWireDiameter = number_input(wireDiameter, 0.1);
+  tick();
+  if (inputWireDiameter == NUMBER_INPUT_BACK) {
+    return;
+  } else {
+    wireDiameter = inputWireDiameter;
+    Serial.print("Selected wire diameter: ");
+    Serial.println(wireDiameter);
+  }
+
+coreLengthStep:
+  lcd.clear();
+  lcd.print("Core length:");
+  lcd.setCursor(14, 1);
+  lcd.print("mm");
+
+  float inputCoreLength = number_input(coreLength, 0.1);
+  tick();
+  if (inputCoreLength == NUMBER_INPUT_BACK) {
+    goto wireDiameterStep;
+  } else {
+    coreLength = inputCoreLength;
+    Serial.print("Selected core length: ");
+    Serial.println(coreLength);
+  }
+
+
+  lcd.clear();
+  lcd.print("Customization done");
+  delay(1000);
+}
+
+void customize_setup() {
+
 }
diff --git a/firmware/src/number_input.cpp b/firmware/src/number_input.cpp
index 6a3fa07..9fc3797 100644
--- a/firmware/src/number_input.cpp
+++ b/firmware/src/number_input.cpp
@@ -2,6 +2,7 @@
 #include "buzzer.h"
 #include "screen.h"
 #include "characters.h"
+#include "number_input.h"
 
 String numberInput = "";
 int8_t dotPosition = -1;
@@ -48,7 +49,14 @@ float number_input(float defaultValue, float encoderStep) {
     auto len = numberInput.length();
     bool isAtLength = len >= MAX_LENGTH;
 
-    if (input.key) {
+    if (input.key == KEY_C || input.switchEvent == SWITCH_RELEASED) {
+      if (numberInput.length() > 0) {
+        lcd.noCursor();
+        return numberInput.toFloat();
+      } else {
+        beep();
+      }
+    } else if (input.key) {
       auto digit = getPressedDigit(input.key);
       if (digit != -1) {
         // append digit (if it fits)
@@ -81,9 +89,8 @@ float number_input(float defaultValue, float encoderStep) {
           beep();
         }
       } else if (input.key == KEY_B) {
-        goto on_back;
-      } else if (input.key == KEY_C) {
-        goto on_continue;
+        lcd.noCursor();
+        return NUMBER_INPUT_BACK;
       } else {
         beep();
       }
@@ -117,19 +124,10 @@ float number_input(float defaultValue, float encoderStep) {
 
       number_input_update();
     } else if (input.switchEvent == SWITCH_RELEASED) {
-      goto on_continue;
     } else if (input.hasInput && input.switchEvent != SWITCH_PRESSED) {
       beep();
     }
   }
-
-on_continue:
-  lcd.noCursor();
-  return numberInput.length() ? numberInput.toFloat() : -1;
-
-on_back:
-  lcd.noCursor();
-  return -1;
 }
 
 
diff --git a/firmware/src/number_input.h b/firmware/src/number_input.h
index e24de76..4084ca1 100644
--- a/firmware/src/number_input.h
+++ b/firmware/src/number_input.h
@@ -1,5 +1,7 @@
 #pragma once
 
+#define NUMBER_INPUT_BACK -1
+
 /**
  * Uses second row of the screen, keyboard, and encoder to get a number from the user.
  *
@@ -9,7 +11,7 @@
  * defaultValue will be truncated to at most 3 decimal places.
  *
  * It will return the number when it's confirmed by encoder press or [C]ontinue.
- * It will return -1 if [B]ack is pressed.
+ * It will return NUMBER_INPUT_BACK if [B]ack is pressed.
  *
  * LCD is set to .noCursor() before returning.
  */