I believe there is an error in this formula. It seems to be taking the miles driven for business divided by total miles and then multiplying that by the fraction of the year the vehicle was used. So if the vehicle was bought or sold in a given year and only used for 6 months out of the year, it would take the business use to total use fraction and multiply it by 0.5. This seems to be a persistent error that hasn't been corrected and is continuing into the current version.
