Novice question about metering

[earth tones]

I'm preparing to calibrate an audio circuit and I need to input a 1K Sine wave at 0dBu = 0.775 VAC.

I have an HP 400E AC Voltmeter with an analog, averaging (RMS) meter.

I also have a Fluke 77 multimeter with an VAC function, that I imagine displays PPM.

I have split an output signal from a Pro Tools function generator plug-in into the two metering devices. When the DMM reads 0.775 VAC, the HP 400E reads 0.79 VAC.

Which of these two devices would be the best to rely on for the 0.775 VAC measurement. Any idea of how I can be sure that the HP 400E is calibrated properly???

[The Scum]

The man with two clocks never knows what time it is.

There are two likely possibilities:
1> The HP is old and out of calibration. You could try to find someone who calibrates test instruments, but that'll cost you more than the meter did.
2> The Fluke is designed for electricians, not audio guys. It might have a high frequency roll off. It's great at 60 Hz, and probably 400 Hz (AC on planes is 400), maybe not so great at 1000 Hz.

Something to try - sweep the frequency of the generator, and see how the two meters track. I'd expect that the HP would read a steady value as you sweep to higher freqs, while the Fluke will fall off.

Try it and report back.