You can calculate the OROP arrears in the following way:
1. Find the Basic pension as per OROP chart- table.
say for Example; Hav and equal Ranks- Sgt- Group- X
As per Table no: 7 of OROP Tables It is = 8585
then as per Cir 501,table No.17..............it is = 6374
Difference per month..... ........= 2211
Now the Effective Date is From 01-07-2014
Arrears from 1-7-2014 to 31-01-2016 will be-
Difference X a factor of 40.53
2211 X 40.53 = 89612/-
SO- 89612 IS THE ARREARS
This will be paid in 4 equal half yearly installments.
For family pensioners, in one installment.
this the simple way of calculation.