   plotter.AddTimeGraph( "Reflow oven variables", 18000, // about 3 minutes
                           "PID Setpoint (°C)", PID_setpoint,
                           "PID Input (°C)", PID_in,
-                          "PID Output (10 ms)", PID_out_by_10,
+                          "PID Output (%)", PID_out_percent,
                           "Oven state (on/off)", oven_is_on);
 
   // Configure PID controller

Thread control_thread = Thread();

// variables for PID controller
double PID_setpoint, PID_in, PID_out, PID_out_by_10;

// for slow PWM:
const int pwm_window = 5000; // 5 seconds


void control_callback(void) {
  // control thread
  PID_setpoint = 50; // constant for testing
  PID_in = measure_temperature();

  control_PID.Compute();
  PID_out_percent = PID_out/pwm_window*100;

  unsigned long now = millis();
  if (now - pwm_start_time > pwm_window) {
