Straight-line depreciation takes the Annual Depreciation divided by the number of depreciable periods as defined in the Depreciation Year in Configuration.

For example:

If an Asset is set to depreciation $1000 in one year and a Depreciation year is set up with 8 periods, using straight-line depreciation will take $1000/8 = $125.00 for each period in that Depreciation year.

For more information on how to calculate Depreciation see How to calculate straight-line depreciation.