I dunno if Im understanding this.

The supervisor can (must) do (at least 1) an onsite visit since stundets visit 0 to 6. If he hasnt done the visit in that lapse by the 7th student visit it would be at fault.

Thats how I read it. In the 10 visits case he must have done an onsite, at least, before the 7th student visit.

And I would say that the statment is false. Cause it may happen that by th 10th visit he only needs one visit, but by the 20th (2 10 visits) he must have gone onsite 3 times at least. Thus breaking the 1 visit per 10 visits.