ffmpeg and ffplay show different max audio volumedetect recommendations

[tas3086]

ffplay -af "volumedetect" shows a max volume of 21.0 recommendation while ffmpeg shows a recommendation of 8.2db
both programs are at the same version/levels. both run against the same input mvk file.
The original file is notably low volume, so Id like to increase it. Any reason why the different numbers? Which number should I use?

[davexnet]

this filter in ffplay displays max and average volume.
These levels are shown in the usual -dB notation

[tas3086]

Correct. Using ffmpeg -i %1 -af "volumedetect" -f null NUL
and
ffplay -i %1 -af "volumedetect"

with the same input file shows the same output levels in the usual -dB notation but with different output -dB values. WHY? Which is the correct?

[davexnet]

I get the same numbers