Chainline is the easiest and cheapest way to improve your track bike performance and drive chain efficiency.
The distance from the center of the frame to the center of the chainring should be 42mm ± 2 mm, depending on your configuration.
Read more about Chainline for Marginal Gains here.
To use this nifty stainless steel tool, just place the V-groove of the gauge on the seat tube. A protrusion indicates 42mm at the center line, and the ± 2 mm tolerance shown by the thick black line running down the indicator.