Another tip
If you need to constantly measure current of various devices and the voltage drop on resistors or in multimeters can screw things up, you can "upgrade" to DC clamp meters or hall effect sensor ICs or current transformers.
With DC clampmeters you don't have to break the circuit, you just put one wire through the middle of the clamp, and you get the current measured. However, the accuracy of the measurement depends on where the wire is positioned inside the area inside the clamp and at low currents DC clamp meters are not so precise. You get maybe 2-5% accuracy when you measure.
Oh.. with dc clampmeters a simple trick can be to just twist the wire around the clamp once or twice to double, triple, etc the current value measured making it easier to measure low currents (but you lose precision).
Here's a good and cheap clampmeter reviewed here on eevblog:
https://www.eevblog.com/forum/testgear/uni-t-ut204-clamp-meter-review-and-tear-down/Hall effect sensor chips are awesome, the internal resistance of such chips is very small (somewhere around 1.2 mOhm or 0.0012 ohm) so the voltage drop is almost inexistent, and the output error is also usually small, at around 1-2% and if you really want super exact measurements you can characterize such chips to know how the output deviates when the temperate is much higher than normal and so on.
An example of such chip would be Allegro ACS712, here's a datasheet :
http://www.allegromicro.com/~/media/Files/Datasheets/ACS712-Datasheet.ashx?la=enDepending on chip, you can measure +/- 5A , +/- 10A , +/- 30A ... basically you power the chip with 5v and it outputs 2.5v at 0A, and goes up or down with a certain number of mV for each A of current, so you can just measure the voltage on the output and convert that value to current.
Such chips work better than some multimeters - some multimeters can measure currents up to 10A but have limitations, like for example they say "measure up to 15 seconds, then wait 5 minutes" or something like that - that's because if the current is high, the internal current shunt heats up and then the value of the current shunt changes and measurements are no longer correct... and if the current shunt heats up too much, it desolders itself from the pcb.
Chips like ACS712 having a fixed 1.2 mOhm (approx) resistance are not affected by this, you really can't push enough current through them for this resistance to overheat the chip.