Measures from the bottom of the unit to whatever you are measuring. I double checked this thing many times with a tape measure and it's always on!!! Good product for a good price!
Fun little tool. Have been using while remodeling a basement. Has been dead on accurate within 1/16 over 32ft spans so far. Overall I think it's pretty cool.
Used mainly for model railroad construction/modifications, but wonderful for all other measurements. Found lots of small wall errors in my house. Love it. Tom
André Grenier 
