The only digital gauges I knew about were the Testo's with the manifold and hoses.
Digi-Cool were the first ones available in quantity, early 2000's. There were a couple of iterations, then the "AK" series were much cheaper. There was a really cool manifold under development, which never happened.
It was all done by Jim Bergmann and his wife. The Digi Cool website is still there with some of the history.
IIRC, he was also involved in the iManifold, but that was bought out a long time ago, and the future of it was unknown. That product was/is liked by refrigeration techs.
There's an app called Measure Quick that can give you real time performance data, which used to be done with a well into 5 figure setup from Honeywell. Jim Bergmann is key in this. I believe he might also be involved with True Tech Tools.
A lot of really useful stuff in Measure Quick is available free.
