20 Khz output

[MrDirect-at-xxxxxxx (by way of Terry Fritz <twftesla-at-xxxxxxxxxx>)]

Hello 

I have a radio shack true rms meter that had a DC voltage measurement.  It 
has a frequency counter up to 2 Mhz.

I am trying to measure the voltage off a DC transformer and it is measuring 
10 volts.  It cannot provide an accurate reading because of the differences 
in frequencies.

The transformer is supposedly -at- 20 Khz.

Does anyone know a formula I might use to determine what the 10 volt 
measurement on the volt meter really is?

Thanks