This is a great way to measure engine termperatures during flight, to callibate your engine instruments, or just to satisfy your curiosity.
Dave Milner has been using this device to gain some insight into the engine in his Vivat motor glider. He used a "standard" CHT ring type sensor (thermocouple):
The logger ( http://www.omega.com/pptst/OM-EL-USB-TC-LCD.html ) is tiny and is self powered. I was able to run the TC wire along the engine mount and around the oil tank and out the oil filler door across 2" of cowling and into the front center of the canopy and then down the panel and onto the seat. I taped the wire down with masking tape so that it could not come loose and tangle in anything.
Before I used it I checked the calibration in boiling water with the boiling temperature adjusted for the actual atmospheric pressure at a Wunderground weather station on the top of the ridge I live on. It was accurate within 0.25 degrees C because It goes up in 0.5 degree steps and it was reading correctly. I then put the logger and cold junction of the TC in the refrigerator while the warm end was still in the boiling water. This changed the reading by less than 1% so I reckon that logger is pretty accurate over quite a wide range of ambient temperatures.
The logger is very easy to use and comes with some software that will export the data to Excel or generate a very nice printable graph in its own format. The result with some notes is attached. You just plug it directly into your computer or laptop.
I want to play with it some more to see what a red line reading on the logger translates to on the gauge - the 260 deg C redline will probably be 280 deg on the gauge. I didn't want to go for broke on the first take off until I had a much better understanding of the relative readings in all phases of flight. Now that I know the cockpit gauge is over reading across the board and it gets worse the higher the temperature I can be more aggressive and climb on the logger indication. I also want to check all 4 cylinders for fun and then check the Zlin too.