It can also be used for confirming the correct preload is still present, with the downside of having to track the original length of every fastener (which isn't really a big deal in high reliability applications)
Which is to say, he wants me to "pre-load the shit out of it".
Which is to say, our "indicator" is that we start to bend the HDB with the threaded rod. For instance, if we have two of these, horizontally, on either end of threaded rod:
https://www.strongtie.com/boltedholdowns_holdowns/hdb_holdow...
... he tells me to tighten that threaded rod between them until we just start to see the hold downs bend (toward each other).
So, not very scientific at all, but easy to tell that you're pre-loaded ...