Can't speak to the Honda 150 or answer your specific question, but do empathize as I've not have not had good luck with trim gauges in general - A 2003 Honda, 2006 Evinrude, and 2014 Tohatsu, all purchased new, and all with trim gauges that worked marginally within the first year or two, due to the little plastic indicator tab that gets stuck or out of alignment in the trim/tilt mechanism.
The best "trim gauge" for me is to look back and see how far the outboard moves when pushing the button one way or the other, while watching your RPMs, GPS speed and boat handling characteristics (i.e. no porpoising). Even when it works I typically ignore the trim gauge. Take it out and put in a volt meter or fuel gauge instead! (haha, just kidding, those are others I never seem to find much faith in).
-Mike