How to calculate Manhours per resource per month for costing purposes

I have made this program where i wanna calculate the manhours per month for various resources, now i look at the group total for budgeted labor hours column and i was able to see that it was showing 113191h but when i tried to input individual manhours from Resource usage spreadsheet or from resource assignment tab the manhours are showing as 113037h which is like 162h difference, can someone tell me why there is a difference? numbers are different in different places..any how that i can make it match? TIA