It is accurate on the flat, when you use the slope measure it seems to only increase the distance by 3 or 4 yards only no matter how steep the incline. When using, I have to keep it away from my face by about 1/2 inch or everything goes black because my eye lashes cover the lens. The eye piece and the lens are nearly level , it could do with a removable eye piece extension. Once you get used to using the rangefinder and ignore the slope adjustment it's good for the money.
It was a gift for someone who is struggling to use it accurately however I have not has a problem using it. I'm sure that once used to this viewfinder she will be OK.