Argyle King
Legend
In case it wasn't clear, that was meant to be somewhat tongue in cheek.
But, if you want the accuracy of tape measures, why then ignore the accuracy when determining LOS and flanking?
And, let's not forget speed of play as well. If you are going to get into tape measures and the like, it does slow play down a lot, unless you are playing with people who are used to it. It's bad enough with hamfisted players bumping minis on a grid, add in tools and it's almost as bad as cats on the table.
I can't speak for others, but I don't ignore that accuracy when determining LOS, and it's really not any different to determine LOS. The main difference is that you don't use the three line rule since you're no longer using a grid, and that rule doesn't make sense anymore. Determine where the target is in relation to the attackers ability to see. If something is partially blocked, it has cover. If the attacker cannot see the target, the attack cannot see the target; just as it would be with a grid.
As for Flanking, the definition of that term is highly dependent upon what game I am playing. However, usually; for me, flanking means either being to the side of the target (giving them a small penalty to their defenses) or behind the target (giving them a significant penalty to their defenses... even if they are aware of the attack.) That does not change without a grid.
As for speed? I've actually seen an increase in speed as people have become more comfortable playing without the grid. After a few sessions, many of the people I play with had become capable of eyeballing a lot of things. Still, for ease of play, I did create a few shape templates for some of the more common area attack shapes and sizes.
Also, a good rule of finger is that the distance from the first line on your index finger to the tip of your finger is roughly an inch. Granted, this doesn't work for everyone as not everyone is built the same way, but it's a quick rule that I learned during wood shop many years ago. It can be applied to tabletop gaming for a quick close-enough measurement for when you don't want to break out sticks or ribbons or rulers.