Yeah, if you have a pressure of something like 0.004, then it will display as 0.00, since it only shows to two decimal places. For comparison, the present day real-world Mars has a pressure of about 0.006. It's closer to being a vacuum than something we would think of as a normal atmosphere, and yet it's enough of an atmosphere that it has weather and a visible sky.
Something I never remember to check is whether the game does normal numerical rounding, or if it always rounds down (truncation). And then you get into the question of whether it rounds toward zero, or does a "floor" operation, on negative numbers. (obviously not for pressure, but for things like axial tilt, etc)