This is the awesome Team Losi Shock Matching Tool.
From the mind of Gil Losi Jr. comes an ingenious new way for 1/5, 1/8 and 1/10 racers to virtually eliminate chassis "tweak" by precisely matching the length and dampening rate of their shocks. To set length, racers attach the shocks to the matching tool and use the easy to read gauge to adjust length. To check lengths are equal all they have to do is make sure the gauge at the bottom of the tool is centered. The matching gauge swinging in the direction of the "weaker" shock during compression will indicate any difference in dampening rate.
The Shock Matching Tool is machined from anodized aluminum with a laser-etched measuring scale on the face. The pivoting gauge on the bottom of the tool is ball bearing supported for maximum precision.