September 7, 2013

A strange formula for cut gem prices

I’m going through adding a bunch of data to this blog’s collectibles information page today and I found some interesting information about the prices of cut gems.  For comparison, real diamond pricing is usually based on the “4C” method; jewelers price their diamonds taking into account the stone’s cut, color, clarity and carat weight.  In The Sims, I was expecting a simpler calculation because only the gem’s stone type, cut pattern and gram weight are displayed.  I was expecting that heavier gems would be priced higher than lighter gems within the same stone and cut categories, following some identifiable pattern.  However, there does not appear to be a direct correlation between a gem’s weight and its price, or if there is, the game allows for some wild exceptions.

For example, the prices that I’m seeing in-game for plumbob cut quartz gems seems reasonable based on the weight:

weight price
91.77 §30
88.05 §28
80.01 §26
69.84 §22
67.80 §22

So the only outliers on this list would be the last two where they are the same price despite a difference of just over 2 grams.  But, that could be attributed to a rounding difference, depending on the formula that is used.

However, I also had a stack of plumbbob cut jade in my sim’s inventory.  The prices for those gems do not appear to follow as consistent a formula.  Here’s what I saw:

weight price
70.08 §398
63.81 §384
39.86 §1,148

WTF?  Why is the third gem at almost half the weight of the other two almost triple their price?  And just to be certain, here are some screenshots of the plumbbob cut jades listed above:




So really, WTF?  I don’t see anything different in any of the descriptions.  Do you see a difference?

In general heavier cut gems will be worth more than lighter weight gems of the same type of stone, but in some cases the weight might not make a difference in the gem’s price.  It almost looks like there is some kind of 4C calculation being made in the game to come up with the price; now if only the game would tell me the missing variables.