SLN function will determine the straight line depreciation of an asset for a single period. The amount you paid for the asset is the @cost, @salvage is the value of the asset at the end of its useful life, and @life is the number of periods over which an the asset is depreciated. This method of deprecition devides the cost evenly over the life of an asset.
The formula used for straight line depriciation is:
Depriciation expense = ( @cost - @salvage_value ) / @life
@cost = cost of an asset when acquired (market value). @salvage_value = amount you get when asset sold at the end of the assets's useful life. @life = anticipated life of an asset.