latency display in jack not accurate?

[chinface]

is it possible that in qjackctl the displayed ms of latency is not accurate?

I've just tried a live stream with the periods/buffer set to (default) and frames at 128, it said the latency was down to 2.9ms, but it was definitely higher than that.
I tried it at 2 periods/buffer and (can't remember the value) frames, it said the ms was 5.8, but the actual latency audibly less than the 2.9 setting i had.