I have asked here a month ago regarding measurement of very low current . I was told that Amper-Meters today has this resistance in series that will cause a voltage dropout ,hence you cant measure a very low current .

So whats happens with my fluk is a very strange thing . if i put it on the scale of 2mA, or even 20mA, and try to measure current in my pcb, i get many resets of the mcu because the voltage is dropped .

But i discovered something else,if i put the scale on the Ampermeter to be in 20A , than the pcb is working and i can measure the current (!).

So my questions are :

1. Why is it working only with a scale of 20A ?
2. are the measurements good? can you count on them ? i can tell that the LCD shows a current of 0.03 in this scale, that means its about 30uA ? (thats what i expect)