The Theme and Plugin Profiler uses a little known PHP feature known as ticks. Basically, this is an internal event that occurs every time a code block is executed, marked (roughly) by a function call or curly {} brackets.
The plugin uses ticks to collect a list of the functions that were executed, how often they were called and how much time they took in total. The plugin’s option page gives some filters to select and sort the results. This will give developers clues which parts of their code demand scrutiny.
