Slideloc is NOT a ruler. You use your ruler to measure then put the slideloc beside it to keep it from moving. I have two sizes but use the shorter one most. I can't tell the lighted one helps any more than the unlighted one. They're not really lighted just how the plastic is cut that makes a reflection. I use the shorter one to square blocks and really like both of them.

Thanks everyone for your input on the Slidelock - it looks like I will be ordering a set'