Add imperial snail

[bjornbm]

I ran into this one at work. 😮

https://www.efunda.com/forum/show_message.cfm?start=1&thread=1&id=30:

When I was working for Lockheed Martin, it was common to refer to mass as "snails". It was developed (I don't know by who) mainly for convenience since structures were usually measured in inches, as opposed to feet. In the feet system, mass is defined as a slug, which has expanded units of lb-sec^2/ft. A snail has units of lb-sec^2/in. Therefore, the formula for a snail is simply:

1 snail = 12 slugs

Mass is a bit confusing when working in the English system because we tend to use lbs for mass, also known as lbm (pound-mass). Pound-mass, which really has a unit of weight, is mass (slug or snail)times the gravitational constant. This is important to remember when entering mass in formulas or programs in the English system. If you're using inches, mass should be entered in snails, not lbm. If using feet, mass is entered in slugs.

As an example, when entering the mass density of a material in a finite element code, a common mistake is to use the density found in handbooks or other references, which are usually listed as weight densities, not mass densities. Therefore, you must first divide the weight density by the gravitational constant before entering into the program. If using inches, divide by 386.1. If using feet, divide by 32.2. The bottom line is make sure you understand which units the formula or program is expecting and that they are consistent.

www.endurasim.com.au/wp-content/uploads/2015/02/EnDuraSim-Engineering-Units.pdf:

Although some have named this mass unit the "slinch" or "blob", we prefer the colloquial name, the "snail". (Thanks to Dr Tim Coates for supplying this useful name for the unit - we are unsure as to whether the term has earlier origins).