Beggining mechanical engineering courses, students learn how to model forces. One of the first things taught is the concept of moments. Moments, in summary, is a force multiplied by a distance from an axis of interest (M = F x L). In order for a system to be static, these moments must balance. 

This is a hands-on representation of balancing a moment equation to achieve a static system. This model consists of a moment-arm (lever) and forces (weights) to act on said arm. There are four notches on each side of the lever axis at an equal increasing unit. The weights provided are scale multiples of eachother (2 small = 1 medium, 3 small = 1 large). 

A further in depth descriptions of moments can be found at https://www.engineeringtoolbox.com/levers-d_1304.html

The parts for this model require 11 grams of filiment. At my filiment price, this equates to 22 cents. A similar instruction tool can be found at a cost of $23 https://www.amazon.com/hand2mind-Student-Balance-Weights-Calibration/dp/B008N17ZGA/ref=pd_sbs_328_25?_encoding=UTF8&pd_rd_i=B008N17ZGA&pd_rd_r=175f77b1-2b76-4771-90ca-af7bbe268da1&pd_rd_w=puGPC&pd_rd_wg=GZPJv&pf_rd_p=52b7592c-2dc9-4ac6-84d4-4bda6360045e&pf_rd_r=K87RTB0WKNX3KADFZ00T&psc=1&refRID=K87RTB0WKNX3KADFZ00T