Newbie confused

[Gordon Palmer]

i have used REW before but not in great depth. i have umik one and cal file installed.
this time I compared the readings to a METERK sound level meter.
irrespective of the relative levels -REW measured the same db at 57 hz and 648hz but the sound meter showed a 13db difference when using a tone generator. The higher frequency was louder and audibly so. Am i missing something obvious?

 

[John Mulcahy]

You can't easily get a sensible reading of level using tones because the level will vary by large amounts even over small distances due to the effects of reflections. Use pink noise (periodic or random) the check levels.