I am not so great on formulas and am trying to set up a numbering system for
documents

Each reference comprises of a 3 letter reference (abbreviated form of
document types) plus a number from 1000 onwards

Eg

ABC1000 onwards
IDAS1000 onwards
QCS1000 onwards

Row A would be the header row and there are 10 abbreviated departments
Each time I wanted to add a doc to the department I would need to choose
next sequential number for that dep

Is there anyone who has any ideas re this?

thanks