I am working on a new project using the MM.FIL units, which is not my normal units set. When I go to add valve weights the units requested are N, I assume Newtons, but this is not a weight (mass) unit, Newtons are a force unit. My valve weights are kg. Why is a force used for a weight?
I am using Caesar II 5.00.7 build 010122.

I suspect this comes from CAESAR's use of pounds for force. In Europe it used to be kg and kp. Now it is kg and N. If you are sending your work to country, which uses metric system I recommend you create your own unit file. Units in CAESAR's mm.fil are not to SI standard. Unit file name needs to be 8.3 style. For the units remove all points, and use kPa, kg/m^3, N/mm or N/m and kg and you will get less comments.

I normally do not get too sophistigated so I just take the given mass in kg * 10 to get that N value (Newton)

C B,

I have the same complaint as you and have voiced it to COADE 2 or 3 times over the past few years.

I guess for now, you can think of it as Newtons-mass and be thankful we don't have to enter RIGID weights as Slugs when using English units.

I don't want to be pedantic but I believe that weight is measurement of force (and should be measured in newtons) and is different from mass. That is why your weight on the moon is different than on earth, but your mass stays the same.

"the dude" is correct, from google, the definition of weight is "the vertical force exerted by a mass as a result of gravity". The Caesar input asks for "rigid weight" and not rigid mass, so Newtons is correct in SI. However, looking at the "English units file" in Caesar, force is defined as lb, which to me is confusing, as mass should be in pounds (lb) and force should be in pounds-force (lbf). The definition/units should be made clearer in the Caesar English units file to prevent this confusion. Almost exclusively I work in SI units, so this confusion does not occur.

If you review the "English" units file distributed with the software you will find:

(lb) -> pound force
(lbm) -> pound mass

(lb) typically refers to "pound force", which is why the CAESAR II units are setup that way.

I do not like to start an other "Unit war". I went through one 1973-1976.

The Random House Dictionary, which I understand is American defines:
lb -> pound, plural lbs.
lbf -> pound-force
lbm -> not listed
pound -> a unit of weight and mass

It gets more interesting when you check weight and mass from the same source.

At least as confucing as we had with kg and kp.

The dude above is correct. In technical literature weight is force (lbf or N) and mass is mass (kg or lb).
According to SI:
1 lb = 0.45359237 kg
1 lbf = 4.44822 N

In any unit set I'm to damned fat!