Is the initial 0.5mm of Deli 30 cm steel rule wrong?
Is this the initial value? Are you mistaken? 0.05mm is the precision, that is to say, the smallest square in the ruler represents the length of 0.05mm, not the starting value of 0.05. Check whether there are 20 squares in one centimeter, so that 1 centimeter divided by 20 equals 0.05.