Well, you wanted an equal-bearing interval method, so this one is not what you want. It's a slide-rule for the 3-bearing equal time interval method. You can still do the same, but it's just a different variable you are measuring. I'm not sure if you were allready aware of it. I think you do. Oh well,
http://www.subsim.com/radioroom/showthread.php?t=147719
(This is the SH3 thread, I also made one in the SH4 section back then, but it's all the same ofcourse)
The formula for the calculation is explained and proven in this document, around page 4.
http://www.filefront.com/17237360/NO...s_Only_TMA.pdf
It certainly seems to lend itself for a fixed bearing interval approach, but only with a digital calculator I fear. Making a sliderule for it would require another extra scale independant from the 2 that the fixed-time interval requires. The fixed bearing interval would require independant scales for both time periods, as wel as one for the size of the bearing interval (which I expect one would not like that to be built-in value). Or reducing the 2 'time' disks to one 'ratio of times'-disk wouldn't help in practice. You'd still have to do the division manually.
I haven't figured out how to construct such a thing. But after I finished working on the above slide-rule I definately thought about trying to implement it too. However the complexity of the formula got the better of me. Maybe it's time to pick up the attempt again. (it certainly beats wasting braincells on 8010)