I will put this here so as to not interfere with the sales thread as such. The first gauge that you have atually looks more like the .22lr gauge. I have a simmilar Eagle Eye gauge, which has the double rings for the .22lr as the roundnosed bullets leave an undersize hole. the smaller ring fits the hole, the larger ring is the scoring size. The .177 gauge has a single ring, as the wadcutter pellets usually used for air rifle and pistol competitions leaves a pretty much fullsized hole. The inner ring on the .22 gauge is actually quite close to correct 4.52mm but not really good enough for estimating scores.
Of course I may be wrong, and it is stamped up as .177/4.52mm
Alan
"If you have a rifle, and you line up back-sight, fore-sight and Frenchman, pull the trigger, the world is suddenly a better place." Bernard Cornwell, in conversation with Mark Urban.