Quality and percentages confusion.

[Orum]

I'm trying to answer what seems like it should be a simple question:

When crafting using 4 legendary quality module 3s (and no speed module influence, i.e. +24.8% quality) and a normal quality recipe, what percentage of the output will be normal quality items?

Based on what the "Tips and Tricks" states about quality, it sounds like it should be this:

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100% (total output) - 24.8% (uncommon) - 2.48% (rare) - 0.248% (epic) - 0.0248% (legendary) = 72.4472%

However, when I test this out in factoriolab, by using a setup with several machines producing, it gives me these various output rates (the individual numbers don't matter, but what does matter is the ratio between them):

• 8.360 (normal)
• 2.376 (uncommon)
• 0.238 (rare)
• 0.024 (epic)
• 0.003 (legendary)

So when you compute the ratio using these numbers, I get ~76%:

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8.36 / (8.36 + 2.376 + 0.238 + 0.024 + 0.003) = ~0.76

...and after asking on Discord, someone using Foreman2 claimed that the normal output percent it reported was 75.2%. So now I have 3 different answers, and they can't all be right, so which is it?

[eugenekay]

Math.Random() is not a guaranteed Lottery ticket.

Your experimental tests came within 1% of the Theoretical values, which is pretty close.

[Orum]

I haven't done any experimental tests, though I'm thinking at this point it may be the only way to actually answer this question.

[Orum]

After doing tests of this in game, I've discovered that the table in the "tips and tricks" is inaccurate, so I'll file a bug report about it (if I can't find one that was already filed).

[Muche]

Also see 116078 "Quality probabilities" tip is misleading, Tips and Tricks Menu: Quality Probabilities.