Low Power??? then i suspect you would mean ones that would use powder the you could class all rimfire as been low power... and ones that don't use powder would be Air rifles.

Yes. 4x - low power magnification is best for scanning objects under a microscope. Why? I honestly don't know but will guess; medium and high power are based off the setting of low power - you don't use coarse adjustment knob for medium and high only fine detail because the coarse is already adjusteded from low.

Engine Position Sensor.

it is 50 on my microscope.............................

The low power objective is small lens with low magnifying power.