Re: How do I figure out the amps/hour usage of a DC air pump?
If you expect to measure current, the current must pass through the meter. That means the meter must be in series with the aerator. If measuring voltage, the meter is in parallel with the battery or aerator.
So to measure current, one lead of the meter goes to the battery plus, the other meter lead goes to the aerator wire that would normally connect directly to the battery plus post.
Most cheap meters that I am familiar with have a separate socket on the meter to measure amps, so you need to check that. Can't help with the settings/display without a picture.
-- Victor Hugo -- "Common sense is in spite of, not the result of, education.”