Conversion statistics appear in two places in the Admin Interface. On the Live or Staging status tab, there is a converting tab that reports the conversion statistics for the current run of the crawler. In the conversion configuration, in the Test It functionality, the report is for the converters run for the one URL being tested.
The Converter Statistics table on the Live or Staging status tab in the converting section provides three sets of numbers: the successful conversions, the unsuccessful conversions, and the conditionals that are tested.
The successful and unsuccessful conversions are separated because they may have very different running times and will give a false impression of the time needed for the converter. Also, it is useful to be able to see at a glance which converters are failing to convert documents. Note that it is normal for there to be failures because documents can be malformed, be misidentified, have copy protection on them, require a password, etc.
The conditionals usually consume very little time. They are reported because it is possible that adding complex conditions that match the body of the data will accidentally start becoming expensive. By reporting them, any problems with the custom conditions you add will be highlighted.
For all three sections of the table, the count of the number of times a conversion step for this converter was executed is reported. Note that this is not the same as the number of documents (of this type) converted because some converters are multi-step (e.g. Email) and each sub-step adds one to the count. On each run the input size (and output size for the successful conversions) is recorded, along with the running time (in ms). Averages of these values as well as the total time (in seconds) is reported.
These numbers come with a few caveats: