Suunto PM-5 clinometer side window

[H Kahl]

It's been years since I used the Suunto clinometer, and frankly even then I never used the side window.  What is it measuring?  I loaned a Suunto to a fisheries guy in our office and apparently he's been taking readings from it for whatever reason.  Hopefully he doesn't have to backtrack too much to get what he needs.  Here's what he said:

"The readings looking through it look too high - for example, if you aim
the clinometer straight up, it reads 180 degrees on the inside versus
the correct 90 degrees on the side. We first noticed it when it read
90 degrees (and 137%) looking through it versus 55 degrees on the outside,
and we weren't looking straight up. The difference is much less (1
degree) at low angles, like 18 degrees."

Thank you for any assistance.  The manual sheet for the unit I have doesn't really discuss the side window.

[H Kahl]

Sorry, we got it straight.  Obviously the scale looking inside the unit isn't degrees!

[BradMarks]

HKahl:  I believe what you have is the %topog clino(PM5/66). The inside scales are % on the left side and the right side is for measuring tree heights at a fixed distance(baseline) of 66'(1 chain).  Whereas the %degree clino has degrees on the left side and % on the right side to measure tree heights at a baseline of 100'.  The baseline of 100' is easier to convert in your head if not standing at 100' from the tree (seldom in the timber type I worked could you be at 100', and precisely 66' was hard to do also at times). For example: an overall reading of 150% standing at 60' makes it a 90' tall tree. I used the %degree for ease of use. I also cruised with prisms, not a Relaskop(which works better in conjunction with the %topog clino). 

[thecfarm]

H Kahl,welcome to the forum.