You already might know about this, but it answers your question about the buttons, not the "8" display. But looks like you can reset the depth finder by removing the positive battery connection.
If you go to the FW site, under customer service, past product information and under past owners manuals, this will bring you to a screen with all product years. Hopefully the links to the Four Winns site doesn't violate any rules.
Here is the link to your boat: Section B, page 7, H has the info on the depth finder
http://assets2.fourwinnsmarketing.com/p ... %20Horizon[SLASH]205-245%20Sundowner[SLASH]2002%20Classic/Manual%20(Complete)%20-%205.3MB.pdf
Dept finder instructions update
http://assets3.fourwinnsmarketing.com/p ... er/VDO.pdf