Edexcel A Level Physics Paper 3: 9PH0 03 - 15th June 2023 [Exam Chat]

The question gives you the absolute uncertainty of the measurements, not the precision of the ruler. With the precision of the ruler, you take half the precision and MULTIPLY by 2 for the absolute uncertainty, then use that to find percentage uncertainty, but because you already have absolute uncertainty, you do not need to do anything with it other than calculate percentage uncertainty.