- A speedometer in a car has a scale of 0-280 km / h, not 0-1000 km / h.

Set range from 0 to 300, no scaling needed

Set range from -30 to 50, no scaling needed

- In my case I want to display current used effect. Maximum in theory is 2300 Watts. It would be nice to have a scale 0-2500 Watt to make it clear and visible. Range 2500 - 10000 will never be used.

- A speedometer in a car has a scale of 0-280 km / h, not 0-1000 km / h.

- Outdoor thermometer has a scale like -30 C to 50 C, not -100 C to 100 C

The idea is to make the scale practical according to the actual case

2) Vibration
Great!
Consider more than an alarm, even think to make it as a confirmation when push a button or when change value on slider. A tick when value change.

Youre doin a great job! It makes it more fun to learn arduino.

1) Scale on instrument
Possible to change scale to any number, not only a multiple of 10. Ex 0 - 200, or 2000 - 3000.

Usually, in real instruments, a scale other than a multiple of 10 is not used, as this is bad for understanding the real value. Can you give an example of what this is for?

This is interesting, add to the development plan

1) Scale on instrument
Possible to change scale to any number, not only a multiple of 10. Ex 0 - 200, or 2000 - 3000.

2) Vibration
An indication that make the device (cellphone) vibrate.