I'm assuming you're measuring somethings' displacement along a scale. There are three simple ways of reducing parallax error in that case: 1: Attach a straight object (like a ruler or straightened...
To help the user avoid this problem, the scale is sometimes printed above a narrow strip of mirror, and the user positions his eye so that the pointer obscures its own reflection. This guarantees...
You get parallax errors with analogue meters if you don't align your eye so that it is perpendicular to the pointer. When this happens the pointer can appear to line up with the wrong mark on the...