Never seen this before , came up while doing a search . TP4: with live constant values ranging from .800 to 1.400 . Reminds me some threshold values like you'd see in some of the Uniden scanners.
Haven't seen this either. But here is a wild thought. Several Radio Shack scanners had a Test-Point 4 (TP4) where you could connect a discriminator tap. Is it possible that display is showing you what the levels are at TP4? Not sure why it would do so, but only thing I could think of.