A bar is actually 14.5 psi [14.5037]
An ATM is 14.7psi @ sea level. [ 14.6959 ]
So, to help those used to using inches of Hg when the given info specs. is in mbar of vac, just multiply the mbar spec. by .0295 and you will have your inch/vac conversion..
Note that a perfect vac [unobtainable. but besides the point] is simply NO air.
Which means that a negitive 1 atm [ Atmosphere pressure-14.7psi] at sea level is equal to 29.92 inches of vac.
Whereas , a 1 bar vac [1000mbar] would only be 29.5 inches of vac. [ the same 1 atm vac in mbar would be 1013 mbar]
I only give this example to help show the difference between ATM and Bar pressure.
Bar is simply another way of psi measurement....but bar/atm are so close a measure that they are often interchanged..