Monthly pension calculation - Details of PPO for one of my colleague

Details of PPO for one of my colleagues are as follows:

Date of joining: 01/07/2001
Date of Exit: 30/04/2018
Date of Birth: 01/05/1960
Eligible Service: 17 Years
Pensionable Service: 16 Years, 10 months
Pensionable Salary: 11,523/-

As per my calculation, he is eligible for a monthly pension of Rs. 2,798/- (11523 * 17/70).

But the PPO states he is eligible for a monthly pension of Rs. 1,824/-.

Can someone inform me where I calculated wrong or how the amount of Rs. 1,824/- was arrived at?

Thanks