I found this review of a Rapala Digital scale on TackleWarehouse. I have questions...

This is why I don't keep a scale in my boat.  They lie.   I can't tell you how many times I've caught a 5.5 to 6 lb fish and the stupid scales calls it a 3 lb 12 oz or something like that.  All scales lie - the Rapala Digital Scale mentioned above is no better or no worse a liar than any other scale, mechanical, digital, whatever.    I won't have one in my boat.

Rulers and bump boards have a similar issue.  They stretch after only a few fish and so a 20 inch fish reads 17 inches.  I get additional mileage out of them by moving the fish's mouth 3 inches off the stop and taking pictures at an angle so it doesn't show.

Its a metrical conspiracy 

   You think that scales is off? Ha! You ought to see how far off my bathroom scales is! I'm only 175 lbs., and it tells me that I'm 220. Now that's a scales that's really off!   ??   jj

1 hour ago, jimmyjoe said:

   You think that scales is off? Ha! You ought to see how far off my bathroom scales is! I'm only 175 lbs., and it tells me that I'm 220. Now that's a scales that's really off!   ??   jj

The only scale you should trust is the ones on a fish..

   I know people who would try this. Never describe a reel as "bulletproof".