Above is a picture of a home-made scale. I took a strand of elastic and attached it to a board. There is a cup to hold the object to be weighed, and a ruler to serve as a scale. The idea behind this scale is that the weight of the object stretches the elastic band (which serves like a spring). Here we nothing in the cup, we see a shadow at the 30 mm mark on the scale. We would call this the tare weight. After we put an object in the cup, we would look for a deflection greater than 30, and then subtract 30 to get a reading. This is the concept of tare in a nutshell. Now we still need to calibrate the scale. So let us just use the US Mint value for the weight of a dime, and use dimes to calibrate our scale.
OK, here is the cup with a single dime. The shadow is now at 31 mm. So we have a deflection of 1 mm for one dime. So if the scale is linear, that two dimes should deflect 2 mm. Let's find out!
OK, with two dimes, we get a deflection of 4 mm? hmmm. We might be able to increase the number of dimes, but we really want low-end-of-the-scale accuracy if we are to measure the weight of matchstick rockets. At best, we are not going to have an accuracy in the rule of much better than a mm, and so, a best we will have an uncertainty of 2-3 grams. We can't fit too many dimes in this cup anyway, so perhaps this is not the best approach. Let's come back to this later.