The voltagebetween power and groung on my board was 4.86 volts.
The voltage across the LED was 2.14 volts.
The voltage across the resistor was 2.6 volts.
So, the voltage across all components was about 4.74 volts.
Ooops! I forgot to measure the voltage across the switch!
When I turned the switch off the voltage was 3.21volts.
When I turned the switch on the voltage was 0.1volts.
Now, the voltage across all components was about 4.84 volts.
In other words, all components used almost voltage in this circuit!
But why was it different between the voltage of switch-on and the voltage of swich-off?