Answer:
A microscope 250 times greater than the regular one.
Explanation:
A scale is a ratio where the numerator is the measure on the map, or the blueprint, divided by the real measure of it. Both on the same units whether on the numerator or denominator.
So if a microscope has a scale of 250:1 then I have a represented microscope 250 times greater than its real measure. Instead of usually reducing it, the scale of 250:1 enlarges this device 250 times.