Its a ship, 270 Meters, trying to align images at scale, the side with the top so i can cut out a profile with the line tool.
It does seem to be snapping in 1m lengths, i think.
I worked out a way around the problem, i removed the template image and dropped it back in in a slightly different position, did that a couple of times until it was placed roughtly where its size would snap pretty much in line with the vertical profile.
Thanks guys.