On Monday, September 4, 2017 at 9:25:51 PM UTC-7, Jeff Liebermann wrote:
On Mon, 4 Sep 2017 14:01:39 -0700 (PDT), wrote:

The professional is the one that's accurate and the cheaper one that was both showing the wrong pressure and probably letting pressure bleed off through the cheaper filler nozzle.

Here's my bicycle pump tester:
http://802.11junk.com/jeffl/pics/bicycles/misc/slides/Bicycle%20pump%20pressure%20gauge.html
I scribbled a little about how it's used in a previous postings:
https://groups.google.com/d/msg/rec.bicycles.tech/YsqvNggfDDM/CoySfXtGAQAJ
https://groups.google.com/d/msg/rec.bicycles.tech/YsqvNggfDDM/XeXJLe5kAQAJ

For a leakdown test, I attach a small pressure vessel to one port, and
pump up the pressure with a bicycle pump attached to the other port.
Then, I watch the pump gauge to see if it remains stable. If the test
gauge leaks, I paint the plumbing with bubble mix looking for the
source of the air leaks. If the gauge itself is suspect, I take it
apart and check the mechanism for leaks.

Well, that certainly seems a better method than getting a good pump to begin with.