Mirror scale
Since a mechanical pointer is slightly raised above the associated scale , it can be seen over different positions of the scale depending on the direction of view. A mirror scale , also a mirror scale, is a device in pointer measuring devices such as voltmeters or ammeters , which is intended to prevent a measurement deviation caused by an oblique view of the scale.
For this purpose, a mirror surface is attached or embedded parallel to the scale surface at the line markings . To read off, you have to hold your head in such a way that the pointer itself and its reflection in the mirror scale exactly overlap. Then it is ensured that one looks perpendicular to the scale and that no parallax error occurs.
The figure on the left shows the case where the pointer is looked at at an angle: You can see a distance between the pointer and its mirror image. Accordingly, the reading on the scale is also incorrect. The figure on the right shows the correct reading if you look exactly perpendicular to the mirror scale.
- Illustration of parallax
Measuring pointer and mirror scale with an oblique view
Measuring pointer and mirror scale with a vertical view
