I am working with the customization of HR module in OpenERP. What are the steps which I should follow to display value in "No of leaves" field of the payslip in HR module?

I have tried different methods like:

1. Allocating leaves to employees
2. Employee requesting for leaves.
3. Employee leaves approved.

Even after the leaves for an employee is approved, the "No of leaves" field in payslip remains zero for that employee.

Have I missed any steps?

Please help!!!!

Thanks