About Feruchemy.

[Fullborn IRL]

Does a large percentage of stored attribute multiply faster than a smaller percentage if both are stored in an equally sized metalmind (but I doubt size of the metalmind has to do with it) for an equal amount of time? Because Feruchemy gives increased returns relative to the initial amount put in shouldn't then say 10% of attribute multiply to something like 11% per hour and 12% multiply at a rate of something like 12% or 13% per hour? Or is it just a linear multiplication of a base number compounded with duration like 75% x 15 hours gives twice as much as 37.5 x 15 hours?

[Treamayne]

4 hours ago, Fullborn IRL said:

Does a large percentage of stored attribute multiply faster than a smaller percentage if both are stored in an equally sized metalmind (but I doubt size of the metalmind has to do with it) for an equal amount of time? Because Feruchemy gives increased returns relative to the initial amount put in shouldn't then say 10% of attribute multiply to something like 11% per hour and 12% multiply at a rate of something like 12% or 13% per hour? Or is it just a linear multiplication of a base number compounded with duration like 75% x 15 hours gives twice as much as 37.5 x 15 hours?

I don't think the size of the metalmind, nor the quantity of investiture stored has anything to do with how you tap that storage or how it compounds when tapped at a ratio greater than 1:1. Here's the WoB:

Spoiler

Sporkify

This is more towards the whole physics stuff, but is Feruchemy really balanced? If it gives diminishing returns, wouldn't this end up as a net loss of power?

Brandon Sanderson

It doesn't diminish. Or, well, it does—but only if you compound it. You get 1 for 1 back, but compounding the power requires an expenditure of the power itself. For instance, if you are weak for one hour, you can gain the lost strength for one hour. But that's not really that much strength. After all, you probably weren't as weak as zero people during that time. So if you want to be as strong as two men, you couldn't do it for a full hour. You'd have to spend some energy to compound, then spend the compounded energy itself.

In more mathematical terms, let's say you spend one hour at 50% strength. You could then spend one hour at 150% strength, or perhaps 25 min at 200% strength, or maybe 10min at 250% strength. Each increment is harder, and therefore 'strains' you more and burns your energy more quickly. And since most Feruchemists don't store at 50% strength, but instead at something like 80% strength (it feels like much more when they do it, but you can't really push the body to that much forced weakness without risking death) you can burn through a few day's strength in a very short time if you aren't careful.

Footnote: This question was asked when fueling Feruchemy with Allomancy had only been seen in Rashek. As such, the term compounding is used purely to reference tapping at a higher rate than can be stored.

So, if you store qty X in Metalmind A and Store qty Y in Metalmind B. Because B is larger y=2x (for the purposes of this example) When you tap either A or B you will still get either 1:1 qty and duration; 2:0.5 qty and duration (with some loss); 4:0.25 qty and duration (with greater loss); etc. until the metalmind is exhausted.

The smaller will simply run out first.