the Canneed "CVG-100 and CVG-200 Canner's Vacuum Gauge",
Used to measure the vacuum pressure of seamed cans. 
The gauge is placed on top of the can and the piercing needle
is forced through the top of the can. 
The rubber collar forms a temporary seal to allow for measurement. 

CVG-100 is designed for using near the product line,
Consists of a 0 to 76cm Hg vacuum gauge, pierce point, and rubber collar. 
Also available with dual scale to measure pressure to 15 psi.

CVG-200 is designed for using in lab, Consists of a holder,
a 0 to 76cm Hg vacuum gauge, pierce point, and rubber collar. 
Also available with dual scale to measure pressure to 15 psi.

Technical data (Changes reserved):
Vacuum range: 0-0.1 Mpa; (0-15 Psi; 0-76 cmHg)
Resolution: 0.005 Mpa
Accuracy: +/-2.5%