I use the airspeed call, in the first instance, to confirm normal acceleration. Mostly, I have a pretty good idea of how far along the runway that I should hear that call. Thus, if I don't hear it by then, I take a quick glance to see if my ASI is registering anything at all.
This has been very useful to me, throughout my career, on critically short runways.
I take "positive rate" from the IVSI. I had one time when PNF made the call while the rate was negative.
I did a momentary double-take on that one!
