In a month with no training events or vacation, for a lineholder:

Block Hours + DHD = Initial Line Credit Value (Line Guarantee)

If you overblock by one minute or more on any leg, your credit will go up by the amount you overblock. However, if you have any cancelled flights, the credit values of the cancelled flights will first wipe out your cumulative overblock time down to whatever your initial line credit value was.

If you start off with a 90 credit hour line, overblock by 5 hours, then have 5 hours of cancellations, you'll be paid 90 hours.

If you start off with a 90 credit hour line, overblock by 5 hours, then have 10 hours of cancellations, you'll still be paid 90 hours.