This is the Performance & Conformity System from PineCar.
FEATURES: 
- Size up your car before race day and increase your winning odds
- Accurately check car weight
- Locate the center of gravity
- Portable, digital scale and conformity gauge keep you up to speed on your racers weight and dimensions
- Instantly check car weight to within .01 of an ounce or .1 gram
- Measure overall width and length, width between wheels, track clearance and locate a cars center of gravity with the handy fulcrum point
- Adjust for optimum speed and stability
- 2 AAA batteries included
- Instructions provided
INCLUDES: 
- One digital scale
- One conformity gauge
- One reference ruler
- Instructions, CoG table, and formulas
Heres how it works:
Used with permission, copyright 1997-2014 Woodland Scenics/Tower Hobbies, Inc.  
Copyright 2014 Brey Corp. t/a Hobby Works.