You can make your own: To make buttermilk, use 1 cup milk and 1 tablespoon lemon juice or white vinegar. Allow it to sit for a few minutes. If you do purchase buttermilk and have extra, freeze it in 1 cup containers or in Ziplock bags. You can also purchase powdered buttermilk in grocery stores.
Straight-line depreciation allows an equal portion of the laptop's cost to be claimed in each year over the total depreciation period. If the cost of the computer was $1,000, for example, then $200 a year can be included in the company's total depreciation amount each year for five years.
However, as with Section 179, your depreciation deduction is reduced by the amount of your personal use of the property. For example, if you use your computer 40% of the time for business and 60% of the time for personal use (such as playing computer games), you can only depreciate 40% of the cost.