Not much info.
What kind of form, single record view, datasheet, main or subform, continuous form?
2 is the number of times used?
Equipment is "entered on the form" how? Can it be that when I see the equipment on the form and navigate away from that record (assuming that's possible) can the value suddenly become 2? Then the right event is the form Current event. Or is the user doing something on that record and as a result, the value is updated and might become 2? Then the form After Update event. Or if the calculation is needed before the record is saved, then the form Before Update event.
There's SO much you haven't revealed!
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.