If student A was absent from AM registration, he will be rightly marked absent by the registration tutor, however lets say student A was present in lesson 1, hence student A's attendance for AM registration should be changed to 'late' rather than absent, as he was not absent for half a day, he was just late by 20 mins.
It will be helpful if iSAMS could automatically identify this and change the absence mark in the AM registration, alternatively notify staff competing lesson 1 or 2 registration, that this student is marked absent in AM registration, do you want to update the AM registration mark!
