Hello Js,

JS>>Why two different values, and why the ones you specified?<<

The voltage drops cross all the resisters and is equal to your Starting voltage when it is done.

For example If you have a 10 volt supply and two resisters across that 10 volts of equal value, each resister will drop 5 volts each.

if one resister is 1000 ohms, and the other is 4000 ohms, together they will drop the full 10 volts, but the 4000 ohm resister will drop 4000/5000 = 4/5*10 = 8 volts. and the little resister will drop 1000/5000 = 1/5 * 10=2 volts. Since you cannot measure anything above 5 volts, you must measure how much you drop over the 2 volt resister.

6.8 and 4.7 total 11.5 ohms

6.8/11.5 * 12volts = 7.1 volts drop
4.7/11.5 * 12volts = 4.9 volts drop

4.9 volts is under your 5 volt limit. Thus you want to measure the voltage drop across your 4.7 ohm resister. 6.8 and 4.7 ohm resisters are not hard to come by...Thus a very good choice of resisters to use.

Dwayne