Andris is spot on. I use a DL1 and love it. I currently take realtime tire temps and that has helped dial in pressures and alignment angles. Unfortunately the $en$or$ and a little on the expen$ive $ide $o I just use three of them and dial in a front and then a rear tire (and set the other side the same).
Caution: Even with the smaller units (DL1, etc) you get a metric sh!t-ton of data. Be prepared for many, many HOURS of getting the hang of the software and finding the actual nugget that you are looking for. I am pretty quick with mine now, but even a few days after the race weekend I'll be going thru more of the data and finding more useful information. With the more expensive stuff, you'll get even MORE data, so be ready with either a DAG (data acquisition geek) or to commit time to it.
I started with the basic DL1 and gps data only. No rpm, no tire temps, no nada. It gave me lat/long G and speed and the extrapolated numbers (time spent accel, time spent decel, degrees per sec turn rate, highest speed, speed at certain points on track, etc etc etc). The 'sector' feature alone really sucks up my time as I examine the track in 6 different sectors and if I did them all perfect then I'd be a half second faster. No car changes, just the loose nut behind the wheel! Literally bucketloads of data.
Before spending money, spend lots of time on the DA forums and reading. Talk to folks at the track who use them and get their impressions.
One thing the DL1 does is coast-down measurements (most prolly do). By taking this information from a highspeed and lowspeed coastdown and inputting some basic info, you can actually get a pretty good indication of what the Cdx is and the rolling resistance, etc.
See this:
http://www.race-technology.com/WebPage2/Ot...tDownCalcs.htmlGood luck,
Costas
cars and such...