It varies, the same as it does for everyone. We do 4 tests most days. It’s not unusual to get 4 out of 4. 3 out of 4 is the minimum we expect. Anything below that is considered an appalling day. I cant give a precise figure but my guts would say comfortably 80%. The majority of DSVA test centres run IRO 50%.
It only needs a couple of 50/50 days and the average is screwed!!
Pete 