PMHow to Prepare a materials purchase budget

When we have to prepare a material purchase budget Generally u follow this:

Sales xxx
ADD closing stock xxx
LESS opening stoc (xxx)

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Production xxx


BUT I FOUND IT ALSO LIKE THIS:

material purchases budget xxx
LESS closing raw material stock (xxx)
ADD opening raw material stock xxx

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material usage budget xxx


While in the first exampe we ADD CLOSING stock , in the second one we deduct them..
Can someone explain me the difference and also where can I find material to learn more about them?