You know, when I initially saw this thing, I thought it was one of the hokeyest things from Harbor Freight, but I used it for the first time this week and I have to admit, it does the job. Draco for some reason had an extra one, so he dropped it off for me to use.
After having the dealer (who shall remain nameless) replace the right front PASM strut on warranty, I noticed the car kept pulling to the right. Using a Stabila bubble level and digital caliper, I measured the right side camber a half degree positive relative to the left (bastard dealer never did an alignment!! The corner balance settings were also upset - coil over lockrings were not at the same height - good thing I recorded the measurements expecting this incompetence) Instead of taking it back, I just readjusted the right side camber myself, adding the half degree negative camber back. This resulted in a toe out condition (steering rack is on the front side on a 996/997) I used to use the line scribe method to measure toe but it requires you to roll the car back and forth a half wheel revolution while trying to look in a tight wheel well at the scribe markings. This method is more accurate if you think your wheels might be bent to any degree.
Feeling pretty lazy, and pretty confident my wheel are still straight, I pulled out the $13 Harbor Freight toe gauge to do a quick front-rear comparison of the toe difference, and surprisingly it was pretty easy to use and I was able to get accurate enough measurements for government work. No more than 5 minutes aligning the gauge on the backside of the wheels, then flipping it around to the frontside to see the difference. Because there's so little ground clearance below my car, use the gauge with the pointers positioned vertically to get an accurate front vs backside difference across a 19" rim. Spec calls for 6' toe in for street alignment, or 0 for track. Using a online camber/toe calculator here, I get about a 1 mm differential front to rear for 6' angle over 20".
http://www.furybusa.org.uk/camber.php
So setting the gauge around the backside of the front wheels, here's the fixed end of the gauge on the right wheel aligned against the tire pointing to the rear side of the rim:
Here's the oppostie side, left front wheel, rear side. The wing screw is loosened, the gauge slides against the tire and positioned against the tire until the pointer goes to 0.
Flip the gauge around to the frontside of the wheels and compare the gap between the tire and the pointer. I left the pointer at 0 on the gauge and adjusted the toe until the gap you see at the top between the pointer and tire is 1 mm.
Thanks Draco!!
