1 atm = 101.3 kPa = 760 mm Hg = 29.92 in Hg = 14.70 psi
pilots know all about pressure...
a bar is 1 standard atmosphere, which is the pressure that on average is exerted on the face of the earth at sea level by the weight of the colum of air above you
standard atmosphere is assumed to be at 15 degrees celcius with 0 humidity at sea level