"Using SMR" translates to Standard Mileage Rate.  As I stated earlier, the SMR *has* a depreciation component in it.  Sorry if I confused you.

(In Lacerte at least)  I always enter the vehicle AND select the straight line depreciation option to avoid future booboos if/when switching to actual vehicle expenses is advantageous.

I have no idea what options PS offers.  Additionally, Lacerte provides warnings that switching to SL is required if business use drops below 50%