Professional e-athletes in South Korea usually have average APM scores around 250-350, but often exceed the 400 mark during intense battle sequences.
While Park Sung-Joon is noted for the record APM of 818, this was measured only during a short time in a game and was probably the result of spamming or holding a key down.
After the release of StarCraft II: Wings of Liberty, many of these metrics were built into the game's interface, including APM, which further popularised the term's usage and served to increase the competitiveness of the game, however, the way APM is measured is slightly different in Brood War remastered than in other softwares, like BWChart, and results in slightly different values (typically higher in ingame Starcraft).
Because of this, more sophisticated measures of APM may attempt to filter out redundant actions by means such as ignoring re-selection of a group of units which was already selected and ignoring the very beginning of the game (when the typical relative lack of action facilitates spamming), in order to only measure a player's "efficient/effective" APM value.
This method has been applied by other softwares later, however, there is currently no standardization of what constitutes an "effective action" and APM is therefore typically recorded without any filtering.