Right, no problem.
A Performance meter is a small device that you place on you dash. they are either battery powered or connect into your car's ciggy lighter. So there is no tricky istallation and it takes about 10 seconds to get them working. They are used to store, display and/or data log your car's performace capabilities. Eg. 0-60,0-100, 0-100-0 1/4 mile, BHP, true speeds, deceleration times, corning Gs, acceration and deceleration Gs. All modern models use GPS and are consequently VERY accurate.
The G Tech SS pictured below can calculated (from pulses in voltage measured through the ciggy ligher) your cars RPM and also has a programable shift light.
The benifits of renting one of these devices opposed to buying them are that they cost a lot of money to buy, while renting is cheap. These are very fun and useful bits of kit but once bought they are not going to be used regulary, unless you are a regular at the track. For example, the GTech SS cost about £200 but to rent would only be about £25 for a week.
There are about 4 main models which range from £120-400 and rental would range from about £20 a week for the cheapest to £60 for the most expensive.
Hope thats made it a bit more clear. If you want more info on what performance meters are have a look at the manufactures websites, see below.
http://www.gtechpro.com/
http://www.driftbox.com/
http://www.race-technology.com/WebPage2 ... ts_en.html