Spot revising

when you're revising a history exam and you only revise parts of the course and ignore the others. For example if you have materials from 1850-1950, you would only choose to spot revise 1850-1900.

I expect a question from the years 1850-1870 instead of across the whole period 1800 to 1900 so I am spot revising facts from 1850-1870.