I have never known glass scales to have that much error, the reason they use glass as there is minimum (no) expansion, it could be in the way it is being interpreted, or calibrated. Is it cumulative?
If cleaning is required, usually the end plate removes to enable the reading head to be slid out, and using optical tissue with pure alcohol, carfully run the tissue over the scale.
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.