Factorio Forums

probability :: double (optional): A value in range [0, 1]. Item or fluid is only given with this probability; otherwise no product is produced. Has no effect when amount is specified.

located here
but when looking at angels bio processing amount and probability are commonly used together successfully(not sure if the resulting product is intended, but not the point). It gives the [amount] of product with [probability] chance. In-game it shows that it will produce [probability]*[amount] of product, which is definitely not correct as it is not guaranteed to produce that, and it is never able to produce that amount (unless probability = 1).

Thanks for the report. I've fixed the wording (the amount part was just incorrect and I deleted it). The in-game tooltip is always a "best guess" as to what it will produce and can never be accurate when RNG is involved.

for other random drops it displays the chance that the item is dropped. Maybe instead of showing a definite number show [amount]x[chance] so its more consistent with other products using `probability` and dousnt give the elusion that it will always drop ([amount]*[chance]) of set item?