Ok so I am a little bit confused here and I am hoping that someone can explain this to me.
So engine/manifold vacuum has always been a never used thing for me in the past. I never really had any experience with it until I started tuning my fuel injection. So all the experience I have with it is from map sensor readings through a data log. All my datastream readings have always been labeled kilopascals. With 100 being no vac/wide open throttle, and 20 being lots of vac during decel. This is how I have learned it and how I am used to it.
So I thought I would pick up a vacuum gauge to check readings on a vehicle I can not data log. Most all the gauges out there I see are in inches of mercury. So we know its tough trying to learn a new unit of measurement (like being used to fahrenheit and having to switch to celsius). So I thought I would search for a vac gauge that was in kpa, but none seem to match. Or they have both in/hg and kpa, but are opposite of how it is done in the data stream of these ecm's.
So looking at gauges, it looks like 0 in/hg is no vac, and 30 is high vac. And if the guage also has kpa on it, it is 0 for no vac, and 100 is high vac. For example, here is a random picture pulled off google: http://www.mityvac.com/hq_images/MVA6178.jpg

So can someone shed some light on this for me?