a low cost air filter restriction indicator gauge for use in conjunction with an internal combustion engine can be achieved by both simplifying individual part configuration and reducing overall part count . more specifically , a simplified design can be achieved by utilizing a one piece base cap which includes a locking extension and reset button integral therewith . by having this part injection moldable , it is easy to fabricate and lower in cost as a complex locking pin assembly can be eliminated . further , the low cost device can be further enhanced by providing a two color visual indicator which displays one color when the device is in its reset position and a second color when the device is in its locked or set position .