I would normally would chime right in with Mac on a discussion about dB requiring a reference value or at minimum SPL, all of the above discussions get a 'pass' from me because they are talking about using SPL meters, which all use 20 micropascals as their reference. There's no way to actually change it on the meters themselves.

It is certainly better form to say 85 dBA SPL than just 85 dBA.

And it has migrated from dB(A) to dBA over the years. Saves some keystrokes is one way to try to look at that positively.

In all my decades of reporting out sound pressure related dB on charts, this would be my standard axis label:

dB(weighting) SPL re 20-6 Pa.

But in a general discussion about output from SPL meters, it's probably o.k. not to put so much detail since there's only 'one kind' of reference in most SPL meters available. Some two channel units can do sound intensity which has a 10-12 Watt reference, if I recall correctly. But by and large the lions share of what are sold as SPL meters use 20 micropascal sound pressure reference.

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