I truly believe the tackle manufacturers are missing a trick here......
Surely a simple, digital gizmo could be developed that clips to a rod ( through which passes the line and as you wind ( say ) running over a wheel ) and gives a reading of the accuracy required. I'm assuming most folk attach the reel to the first joint of a rod when adding line to a reel (?), but even if they don't now they could with this ingenious idea ! ( winky smilie here ! )
Maybe it needs to be something similar to a bite alarm sort of thing where line moving over a wheel sets off the alarm ( well, my old jobies do, anyway ! ) and this I'm sure could incorporate a digital scale reading off in metres.. This gizmo could be attached to the rod between the first and second ring for example with the line running over it or through it, under built in minimal, adjustable tension....
No, I'm not saying I have it dead right, but something along the above lines would work for all types of reel as it only needs the rod section to make it work......
I'm quite sure most anglers ( even those who have cobbled up systems at the moment ) would buy one as it would totally removes the inaccuracy problem as outlined by the OP............It wouldn't need to be a cheapo IMO as it's value to a fisherman would far out way the initial cost !
Any of you bright sparks able to enlarge on this - either that, or shoot it down in flames !!
As a long time retired engineer I can easily see this animal having legs - it just needs someone like Fox to develop it.........................IMHO
I just don't know where these wonderful ideas come from - they just pop into my head from time to time !! Hohohoho..