Performance-monitoring tools have long been an essential part of the developer’s toolset. The limitation of those tools, however, is that they could only give you part of the picture of how your application runs. Each tool gave only a piece of the puzzle, and there was no easy way to compare data between tools to see a complete view of the your application’s behavior. Instruments in Mac OS X changes all that. It allows you to see multiple aspects of your application’s performance over time. With time-based graphs, you can monitor CPU usage, disk I/O, and memory usage and see how they interact. If your application crashes or starts to bog down, Instruments can show you where, when, and why with the click of a mouse, jumping straight to the offending line of code.