dear
these are terms used in bonus act to decide the percentage of bonus to be paid to employees.
set on--first we calculate allocable surplus and out of that surplus we pay bonus and after paying max bonus ie 20% ,if some amount left balance is called set on and this amount is kept in reserve for future .
set off-if in any accounting year you donot have sufficient surplus and even you are not able to pay minimum bonus of 8.33% than legally you have to pay 8.33%,so balance amount which u donot have in surplus will be shown as set off for future
and you have to take care of set off/on in future before deciding rate of bonus.
tks
j s malik