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U1273A mV range problem

Question asked by tapanther on Dec 29, 2011
I just got my U1273A multimeter, and I was testing it out with some sample circuits I had lying around. I had a 555 astable timer circuit with a lowpass filter across the output. On my oscilloscope, I read 18mV RMS voltage after the filter (pretty good sine wave). On the mV range that has the LPF option, I read 18mV as well with the LPF off. On the normal Volt range (set to AC), I also read 18mV. However when I use the normal mV function set to AC, I get 0.270 mV on the 30mV range, and 2.90mv on the 300mV range. The oscilloscope however always shows 18mV, even with the meter connected. I can't understand why one range is accurate (LPF mV range with LPF off) while the other is completely useless (normal mV range). Can anyone explain why this is?