Spells cost reduction

[Nikich]

Hi. I'm creating a mage, and i'm trying to get to know how the spells cost reduction works. So, for example, i have a spell of lvl 15. The description says, for example :"Cost : 2, 1 to maintain." In this case i cast it for 1, and just maintain it for free. But what if it says :"Cost : 3, half for maintenance." Do i reduce only 3 to 2, and get 1 to maintain, or i reduce 3 to 2, get halved value, so it's 1 now, and then i reduce it too, so it's free now?

[finn]

First, you halve the casting cost to determine the original maintenance cost. Then you reduce the maintenance cost by 1 for high skill.

This means you would halve the casting cost of 3 by 2 to get a original maintenance cost of 1 (you round down). You would reduce that by 1 for high skill and maintain it for free.

[Nikich]

Originally Posted by finn

First, you halve the casting cost to determine the original maintenance cost. Then you reduce the maintenance cost by 1 for high skill.

This means you would halve the casting cost of 3 by 2 to get a original maintenance cost of 1 (you round down). You would reduce that by 1 for high skill and maintain it for free.

Oh, so if it is 4 to cast, then 2 to maintain - 3 to cast, 1 to maintain. Didn't know that for odd numbers it rounds down. Is it written somewhere? Haven't found anything about it.

[finn]

Originally Posted by Nikich

Didn't know that for odd numbers it rounds down. Is it written somewhere? Haven't found anything about it.

I tried to look that up before making my previous post, and the only reference I found was page 9 of Characters. I read it as "everything is rounded down, except for point cost of character traits, unless explicitly noted".

[ericbsmith]

Originally Posted by finn

I tried to look that up before making my previous post, and the only reference I found was page 9 of Characters. I read it as "everything is rounded down, except for point cost of character traits, unless explicitly noted".

Good grief, this sounds like one for the errata. You are correct in what you said, no doubt, but every time rounding is mentioned in connection to casting cost it always says to round up. Unfortunately, the term used in connection with maintenance cost "half that" appears 68 times in GURPS Magic while "round up" only 21 times (and not all of them in connection to casting cost). I think the intention is that casting costs should be rounded up, but that intention is poorly executed - which isn't the only thing poorly executed in GURPS Magic.

[finn]

I had not gone through looking for examples in the spell list when I wrote my response. looking at some examples, I agree that it is likely that the intention of "half that to maintain" is to round up.

Rounding of half costs only becomes an issue when (1) the casting cost is variable, and can be an odd number, (2) the maintenance cost is "half that", and (3) the spell description does not mention to round up.

In these cases, whether to round up or down should be the GM's call. If I was the GM, I am likely to round up, because (a) I don't want to waste time during the game to check if a particular spell rounds up or down, and (b) I feel a little unconfutable that a caster with less than skill 15 could maintain some spells at "1 to cast" level for free.

[kirbwarrior]

Originally Posted by ericbsmith

Unfortunately, the term used in connection with maintenance cost "half that" appears 68 times in GURPS Magic while "round up" only 21 times (and not all of them in connection to casting cost). I think the intention is that casting costs should be rounded up, but that intention is poorly executed - which isn't the only thing poorly executed in GURPS Magic.

Linguistic logic would imply to round down normally because rounding up is explicitly called out. I'm not leaning towards that as a GM, but just thought I'd point it out. You are definitely correct in the poor execution of intent.

[Rupert]

I go with rounding up, for the same reason that things like FP costs for powers are rounded up, and things like major wound thresholds are rounded up. That is, when you pay half of 3FP (for example), you have to pay at least 1.5FP, so you actually pay 2FP because FP aren't divisible. It's the same as why a major wound rounds up "more than half your HP" means doing 6 damage if you have 11HP. You don't get a discount, but must pay the full price.

[SQBlack]

I know this is a zombie thread, but there seems to me to be another interpretation that can be applied to the "half that to maintain" spells. Every single one of those spells has a duration of at least 1 minute, so we're not worried about FP loss for maintenance on combat time scales. At that point, maintenance cost becomes a rate, not so much a "pay it now" kind of thing.

So if a spell has a duration of 1 minute, costs 1 FP to cast, and half that to maintain (I'm looking at you, Simple Illusion), then it can be maintained for a cost of 1 FP per two minutes. Maintaining it for 12 minutes, for example, costs 6 FP.

If a 1-minute spell costs 3 FP to cast and half that to maintain, then that's 3 FP per two minutes for maintenance. Maintaining it for 12 minutes costs 18 FP.

"Round up" then really means the same thing as "pay each individual FP in advance," which is what we all do anyway. If a spell is 2 FP to cast for 1 minute, and 1 FP to maintain, then of course we expect that 1 FP to be paid at the start of the second minute.

That's also consistent with B9, which says "round up for point costs." It doesn't actually say "character points"; I think it's reasonable to use it for fatigue point costs too.

That means I'd handle something like digging a hole in hard soil (B351) exactly the same way as I would maintenance cost on a spell. It's 3 FP per hour, which really means 1 FP for each 20 minutes. If someone digs for an hour and a half, I'd charge them 5 FP.

I can see someone interpreting B9 the other way, but that would only make a difference of at most 1 FP (basically, do you pay for each 1 FP period in advance or at the end or halfway through).

In short, maintaining Simple Illusion at skill 14 for 10 minutes should definitely take 5 FP, not 0 FP (which is what happens if you round down each minute's maintenance) or 10 FP (which is what happens if you round up each minute's maintenance).