Buying charts? Then a chart audit is a must. What's most important is how many patients have visited the practice at least twice in the last 12 months. Then you want to know how many have been in only once in the last year, twice in the past two years, once in the past two years, etc. From there a formula can be devised to give value to each type of patient/chart. You could also value the charts at somewhere around 40% to 50% of collections.