How do DAW's report input and output latency?

I’ve been wondering, how do DAW’s report input and output latency without sending audio out for a round trip test? Is it just an arbitrary estimate? I’m talking about the values given in a device setup screen (sample rate and block size settings).

Any pointers on how to do this (if they aren’t arbitrary values that is) would be very much appreciated.

Some driver systems have a way to query that. The reported values may of course be completely wrong. The DAW should additionally allow the user to manually adjust the figures.

Juce’s AudioIODevice provides the methods
getInputLatencyInSamples and getOutputLatencyInSamples.