What is "30 Days Average" for "Daily Salary based on" in Payroll Module Setup?

When 30 Days Average is selected in Daily Salary based on, the daily salary will be calculated as: 

For complete worked month: Monthly Salary / 30 

For incomplete worked month: Monthly Salary / 30 x RoundToInteger (30 x Days between the start date and end date / no. of days of the months) 

e.g. Termination Date at Jan 2, pay for 2 days,  30 x 2 / 31  = pay  1.935 days = round up to 2 days = $2000

e.g. Termination Date at Jan 30, pay for 30 days, 30 x 30/31 = pay 29.032 days = round up to 30 days = $30000

e.g. Termination Date at Jan 31, pay for 31 days, 30 x 31/31= pay 30 days = $30000

Remarks:

1. When 30 Days Average is turned on, Payroll Considers Appointment History cannot be turned on as Payroll Considers Appointment History required calculating the exact calendar date.