From what I have read and been told .You should NOT weigh any fish you plan on releasing.
Just my .02
I have Cabelas spring scale that works well.
I could have sworn I made a post on this to I'm In, oh well, maybe I did elsewhere ??? I did some research and you are 100% correct, "fish to be released should not be weighed by coventional methods we use". I'll see if I can pick out some highlights from F and G biologist and post it here, he had allot to say on the subject. The drops they put in the water are a controled substance, forget that idea, people would be smoking it, lol.