lbm is not a unit of force, which you need for pressure. it looks weird because it's translated from mass to force. Example in metric:
Newton is (kilogram * meter) / second square. So to express unit of pressure with unit of mass you would have (Kg*m/sec^2)/mm^2
Meter / milimeter square would reduce to a numerical factor 10^6 / mm, so you end up with (Kg*/sec^2)/mm which equals to Kg/mm*sec^2, disregarding the numerical factor of 10^6.
This is the reason some of these units look weird.
BTW, when creating new materials, you do not have to insert values you don't need. Sometimes I only use density field, but mostly density, poisson's ratio, modulus of elasticity and tensile.
Hope this helped.
EDIT:
Dampening unit of sec / in would be an inverse of velocity.
lbm/(in*sec^2) is derived from lbm * acceleration of gravity / surface area . Units are: lbm * (in/sec^2) / in^2 which is equal to lbm*in / in^2 * sec^2.
in / in^2 = 1/in so we get lbm/(in*sec^2)
P.S. You can make it easier on yourself by changing units in drop down box, it will allow you to input these values in any unit you like.
