Take your salary, divide it by 80 and multiply by 27,= annual gross salary. To calc lump sum, take salary, multiply by 1.5, divide by 40 and multiply by 27.
Ansd here's another question; if you take unpaid term-time in the year of retirement, I presume the full yearly salary is used in the cacl.?
AFAIK its the Salary Point you are on that counts. Not the amount earned.