## How to calculate the accuracy of a map

I got such question:

When using an ordnance survey map calculate the accuracy to which each of the distances can be measured when scale of the map is:
1) 1:500
2) 1:1250

I think I know answers:
1) 0,5:250
2) 0,5:625
but I don't know how to calculate it.
I would be grateful for any help.