The first choice is the standard weight calculation formula passed down to us from the ancients. It is a formula that can be used to calculate other fish species simply by changing the value 800 to something else. [eg. 750 for Steelhead, 650 for Salmon, 1200 for Panfish etc.]Ramsell/Wilkinson Formula
The second algorithm I chose to include is a formula developed by World renowned Musky Historian Larry Ramsel and Warren Wilkinson. It was their contention that the standard accepted formula over-estimated the weight on trophy sized muskellunge. Hence his refinement of the accepted Standard Formula.Casselman and Crossman Formula
The third formula was developed by researchers Casselman and Crossman who derived their algorithm via linear measurements and weight data from 341 "trophy" muskellunge. Although the formula is shown here in its original metric form, you can input the dimensions in inches and your result will be in pounds as the metric/imperial conversion has been coded into the algorithm.
Using all three algorithms on the same fish will give you a pretty good range to go by. Instead of potentially damaging a fish more by hoisting it up on a scale, or whatever, just get a good seamstress measuring tape and get some quick, accurate measurements. The less time the fish spends out of water, the better its chance for survival after release.
Of recent note: Tom Betka is working with Larry Ramsell on developing a P.C. program that does weight calculations, implementing some changes to the calculations. Details can be found here ... www.esoxhunter.com/weightform.php