follow these steps:
Start by cutting a strip of paper or cardstock to a length of 50mm. This will be the base of your scale.
On the left side of the strip, mark a point at the 0mm mark, this will be the starting point of your scale.
Using a ruler, mark off 10mm increments to the right. You will have a total of 5 marks (10mm, 20mm, 30mm, 40mm, and 50mm)
At the 30mm mark, mark a point that is 3mm to the right of the 30mm mark, this will be the end of your scale.
Lastly, use a ruler to divide each 10mm segment into 1mm increments. You will have a total of 30mm on your scale that can be read to 1mm.
Your scale should look like this:
0mm | 10mm | 20mm | 30mm | 30.3mm | 40mm | 50mm
It's important to note that this a plain scale and it does not have any graduation marks on it, it is intended to be used as a reference to measure the length of an object and compare it with the scale.