Found a new Digital test guage

I wanted to get a true reading of my regulator on my Impact so I looked into a digital guage. I found one for $100 dollars and it included free shipping. It has a 1/4 npt male end I found an adapter 1/8 bss to 1/4 npt for around $10.00 dollars . The Gauge was from www.automationdirect.com the fitting is from www.hydraulicsdirect.com. You will have to take a little off of the bottom of the fitting so it will seal well. I used a lathe but you could use a file just keep it square. I found that my FX guage is off almost 10 bar.
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I'm kind of a tool junkie was going to buy one of the super expensive ones but didn't feel I would get the use out of it to make the price ok. So I started looking for a cheap one. I found these and did some research on them. Found a lot of people who were very happy with them. It took a while to find an adapter from British to NPT but I did and had everything in a week. However if you order one I would get the 0 to 5,000 PSI They are the same price. I bought the 0 to 3,000 PSI it works but would have liked the higher pressure guage then I could use it on my compressor.

 
Hi guys

Just a thought re my Crown.
My scuba tank has gauge checked, within 2 or 3 bar accurate.
Fill gun reservoir gauge agrees with scuba gauge.
If Reg below setting, mine reads 130 bar max. So let reservoir and reg fall below 130 say 120. Fill gun to 130 , scuba tank reads 130 and Reg gauge 130. Must mean they are all within scuba tank variation eg 2 to 3 bar. 
Am I missing something here?

safe shooting