Scanmasters display the info being fed to the ECM. They display your 02 sensor mv number and if any timing is being pulled by the engine. These can (but not always) show if you're running rich/lean and if there's any potential knock going on. A proper air/fuel ratio is critical on a turbo car.
The Scanmaster can also show your vehicle speed, engine rpm, coolant temp, IAC position, malfunction codes (no more having to do the "SES light count" when the SES light comes on), battery voltage at the ECM, etc.
And if you happen to have a a powerlogger, the Scanmaster can also show boost readings, wideband readings, spark advance, pulsewidth, EGT, etc. But you need to have the special chip that comes with the powerlogger for this to work and you also need to have the powerlogger hooked up to a wideband as well as the MAP sensor. Plus the Scanmaster with the 2.2 chip from the powerlogger will read faster in real time (unlike the version 2.1 that changes every 1.5 seconds). Plus the wideband (usually) gives more accurate lean/rich numbers as opposed to the narrowband the Scanmaster displays in stock form.
Full Throttle Speed and Turbo Tweak both sell the Scanamster, the 2.1 version. You can also find Scanmasters used in the for sale section here. Get the 2.1 version if you can.
