TimeUsed[] gives the total number of seconds of CPU time used so far in the current Mathematica session.

"How to" Topics Building Up Calculations Lists

Create Animations Build an Interactive Application Import and Export Animations

Types of Numbers Complex Numbers Numeric Quantities

CheckAbort[expr, failexpr] evaluates expr, returning failexpr if an abort occurs.

Introduction to Dynamic Advanced Dynamic Functionality

MatchLocalNames is an option for Trace and related functions that specifies whether symbols such as x should match symbols with local names of the form x$nnn.

Pause[n] pauses for at least n seconds.

UsingFrontEnd[expr] evaluates expr, making use of a front end if necessary.

$Aborted is a special symbol that is returned as the result from a calculation that has been aborted.