Formula for Service Level Calculation

Does anyone know the exact formula use in getting the Service Level?

It was explained to me as the following:

S = (T/(H+A))100

Service level equals total answered calls within threshold divided by total calls answered and abandoned. That x100 just converts it into the percentage, otherwise you end up with 0.045 or something like that.

BP service level is calculated as Handled in Service Level/Abandoned Outside of Service Level