Understanding Percentage Calculation

The main output of the tv_process program consists of an analysis of each of the possibly affected stations found in the FCC database.  Each analysis can have a number of "Scenarios" which are considered (with different combinations of stations found in the database).  Each scenario has a "Before" and "After" case and the pass/fail status of a scenario is determined by the percentage increase of interference.  The way these percentages are determined is not obvious in all cases.  Here is a brief description of how theses percentages are calculated (thanks to Bill Meintel for this text):

Get the difference in the total interference caused (before and after study) then divide it by the baseline. For analog stations it is easy - the baseline is the population inside the contour (the value on the first line in the individual results). Determining the baseline for a DTV is the tricky part. If the affected DTV station is operating on its original allotted channel then the baseline is the greater of two numbers - its original DTV service or its original analog service (as they were in 1998). The original DTV allotment service is the actual predicted service at the time the table was finalized in 1998 - in other words the terrain limited service (2nd line in the results) minus all interference. The 1998 analog service is the terrain limited service (2nd line in the results) minus only the analog interference (not the total interference). These results will appear in at the beginning of the analysis for a specific DTV station; however, if there is more than one record for the station they will only appear in the analysis for the first record encountered so you may need to search backward through the report to find those results. If the DTV station is not operating on its original allotted channel then the baseline is the service (terrain limited service minus all interference) in the before study for each scenario. The baselines for the LPTV's are simplified since we don't have to deal with any original allotments. The interference to the analogs are the same as the full service and the DTV's are the same as the full service DTV's that are not operating on their allotted channel.