I'm on vacation so I don't have my owner's manual with me, but I'll take a
look at it when I get home. In the meantime, where do I start?
Troubleshooting my depth guage, that is.

I'm getting a readout of 1.5 feet in depths that are certainly within the
range of my instrument, but are much deeper than 1.5 feet. And when it's
not reading 1.5 feet it's reading the correct depth. Where am I most likely
to find my transponder (?)? Etc. I'm assuming the first thing I do is
check for debris.

2005 Sea Ray 185 Sport
4.3L efi Alpha One Mercruiser

By the way, just had a great BBQ beef sandwich at Brad's in Pismo Beach.

Thanks