How things work:
Amp meters, by definition are suppose to be low resistance items.
When you're measuring current through a circuit, you don't want
to waste any of the available voltage across the meter.

As an example of this, current shunts for meters are usually rated
at X-amps for 50-100 mV across the shunt.

On the other hand, volt meters are put in parallel with a load, and
to be accurate, they should be many time higher than the load
resistance so they don't pull the supply voltage down that you're
trying to measure.

Back in the "good old days" for example, they would specify taking
a voltage reading with a "minimum 20K ohms/volt" meter.
If your trying to measure 100 volts, if you have a 150 volt range
on the meter, this would be a load resistance of 3 megohms across
the circuit you're measuring.

In the example given for a 250 uA meter, that's only 4K/volt.
But for measuring 10-15 volts, most supplies are good for anywhere
from 1-25 amps, so the extra 250 uA is hardly noticeable.

--
Jeff-1.0
wa6fwi
http://www.foxsmercantile.com