82 total clients
2 did NOT get a checkup
(82 - 2) = 80 clients DID get a checkup
80/82 = 0.97561 = 97.561% of your clients have had their checkup.
Interestingly, that's the exact same percentage of your clients who have had lunch. Perhaps ... I'm not stating this as a fact, but it's a hunch ... just maybe the other two have not had their checkups yet because they are out getting lunch.