Factorio Forums

The Factoriopedia page called "Quality probabilities" shows how quality levels can be skipped (e.g. tier 1 --> tier 3) with a reduced chance. The table implies that the chance of going up one tier is X, two tiers is X^2, three tiers is X^3, et cetera.

After doing some testing, I found out that the proability of going up two tiers is always 0.1*X. Three tiers is 0.01*X. Four tiers is 0.001*X.

This seems arbitrary and there is no indication anywhere of a hardcoded value of 10%. It also removes the increasing benefit from having a greater quality % from a machine, since the chances of skipping tiers are lower than they would be for X, X^2, X^3, X^4.

myridium wrote: Wed Aug 13, 2025 2:08 amThis seems arbitrary and there is no indication anywhere of a hardcoded value of 10%.

quality/prototypes/quality.lua specifies next_probability = 0.1, for Uncommon - Epic levels.

QualityPrototype definition says:

next_probability :: double optional

Default: 0

The quality effect of the module is multiplied by this. For example, if a module's quality effect is 0.2 and the current quality's next_probability is 0.1, then the chance to get the next quality item is 2%.

Must be in range [0, 1.0].

Good Luck!