Most Gauges Are "Horrible"
I hear daily of engines being destroyed by people relying on gauges. I have run hundreds of accuracy tests on practically every inexpensive aftermarket gauge under $125 offered. Practically all read low in the 212 to 260 degree range by 40 to 50 degrees on oil temperature and head temperature gauges in the 250 to 550 degree reading range, again being low by as much as 250 or more degrees. I tested about twenty each of most brands such as VDO, Smith, Stewart Warner, Hawk, etc., and found none without these problems.
Oil temperature gauge readings would be 212 to 220 degrees on the gauge when the true test temperature was 240 to 260 degrees. Head temperature gauges read 385 degrees with a true test temperature of 550 plus degrees. When head test temperatures were upped to 700 degrees, the reading of the gauge went up to 390 to 395 degrees. The price range of such gauges was from $60 to $125. I swapped gauges with senders and got different readings. I found nothing in that price range I would wish on my worst enemy. Not one I tested could ever be properly calibrated or relied on in any way for any valid information or even as a comparison from day to day on the air cooled VW. Yes, even the oil pressure gauges were just as bad.
I found good accurate gauges range from about $250 to $350 and few people would buy them. What was needed was a device that gave the information required and was reasonably priced. That was the reason for the GB 227 in the first place. It is specifically made and calibrated to provide an accurate reading in the ranges of the VW air cooled engine. Originated by Hal Brown in 1972. Made in the USA.
Note: If you must install an oil pressure gauge use GB 264-1/8 tee fitting and GB 265-1/8 pipe nipple to install the factory (Bosch VWA021-919-081B) light sending unit and the gauge together as the factory sender and light are over 100 times as fast to tell you if you run out of oil. Never use any sender that has the pressure and a light combination as they are extremely slow and you lose the rapid action that the factory light sender provides.
Warning: If you want gauges as a decoration fine, but never rely on them. After all, if they provided reliable information I would be selling them to make a profit just like our competition.