Can you create an "Earnings Item" so that it appears in units other than hours?
The first payslip needs to show $90 per unit x 11 units = $990 gross pay
(31.5 hrs work - Average $31.42857 per hr)
The second payslip needs to show $90 per unit x 10 units = $900 gross pay
(29.25 hrs work - Average $30.76923 per hr)
The gross pay is NOT calculated based on hours.