In a previous entry, I mentioned how accurate Plan13 is. Recently, I collected side-by-side data from plan-13 and the respected Predict program and compared their results for satellite latitude and longitude. A day's worth of data regarding CO-57, a low and fast-moving satellite, resulted in a worst-case difference of 39.5 km between plan-13's predicted latitude and longitude and that of Predict. On average, the difference was 14.5 km.
(The actual results might be better than this. Since both programs were called independently and each refer to the system real-time clock, it is likely that occasionally the real-time clock turned over a second between one program running and the other. ) Here's the worked spreadsheet file in OpenOffice format.