The name says it all, except that there is a Sharpieâ„¢ marker included if you want to make permanent notes on this flat and writable tape measure that also works with a pencil for temporary notes.
If you measure the light output at a given distance before your client is in front of you, then later when you are really shooting, it's easy to always get the exact right exposure without a lot of light-meter readings and extra flashes at your subject.