A ruler that fits in your wallet

This project includes 2 small rulers, both designed with 2 sides measuring lengths in centimeters, 1 side measuring inches, and a protractor in the middle.
One is the free size 96*60mm, the largest free size in this ratio.
The other is the size of a credit card and ID card, making it easy to put in a wallet and use.
 
The white one on the cover is an aluminum-based ruler, which can be made by simply removing everything on the bottom or top.
 
This ruler has made its best efforts for the convenience of use and has the following features:
1. The scale ruler has marking holes at integer positions;
2. Due to the inaccuracy of the silk screen position during the production process, solder mask is used to open the ruler.
3. The ruler scale is calculated from the edge, and the accuracy error is controlled by whether to use ordinary gongs or fine gongs. The error parameter given by the manufacturer is 0.1-0.2mm, which is sufficient for millimeter scales . ;
4. The protractor adopts the method of opening the window multiple times to ensure that the zero scale is within the window, and a marking hole is also drilled at the center of the circle.