Reel Line measurers?

[mvtek]

I agree with Rev. Blade, knots will weaken the line. One suggestion might be to use some different colored "whip" line at the desired distance. Using a needle you can pierce the line once to prevent slipping up or down the line. For those not familiar, "Whipping" is a method used to prevent the end of a line from unraveling by using a smaller (thinner) line to wrap it. Just my 2 cents.

 

[Rick Murchison]

"Knots as weak spots" is a red herring. The kind of line use in diving we're talking about here doesn't test the tensile strength of the line; in an abrasion-free world a stout sewing thread would be strong enough, even knotted. If you're pulling on the line with more than about a pound (half a kilo) of force you're misusing it.
There are two principle uses for line -
(1) guideline in an overhead environment or in poor visibility, and
(2) deco line
When used as a guideline only enough tension to prevent tangling is used; when used as a deco line only enough tension to keep it nice and straight is used.
Personally, I put three knots about a half inch apart at 10 feet, two at 20 feet and one at each ten foot increment after that. I put two knots about an inch apart at each 50 foot increment. Knot pattern schemes are personal and varied - mine works for me. The advantage of using knots over most other marking is that you can use 'em in zero visibility.
Rick