Seems to me if you placed a level in your boat's floor made the boat as level as possible then used one of these or a better product you could get the dead rise quite easy at any point on the hull.

https://www.homedepot.com/p/Johnson-...-700/100161689

The newer 21 is supposedly just a shorter 23.

Used a level and protractor to eyeball my '88 18' today after reading this thread.
Looks like 20, 14, and 10, as near as I can tell.

Use Iphone to Measure Step Angle
 

I have used my Iphone 6s both as a level and a protracter. Also used it taped to the AV plate (in the driveway) to determine trim angle versus my trim gage. Just tried the iphone upside down and it still reads. Turn on the compass app and sweep your finger quickly from one side to the other to turn on the level. It will read the angle in two directions, so you my have to play with it to get the desired angle.

That would be the same as the 23 and less than the 20.

I measured this on my 1975 20 foot master angler and redrew in CAD

This is a lines plan I was given to work on in the late '80's

Island Marine Group

THIS...for the newer 21 that went into production in 1998, Tracker...built by Silver King

Joe R.
21 SeaCraft
Susie 2

If you park it on a hill you can just measure both sides, add the two numbers together and then divide by 2.

There ya go Big.....being average and making way too much sense!!! :)