[Enhanced Senses] Normal Senses and Modifiers Confusion

[Humabout]

On GURPS Powers - Enhanced Senses, p. 9 under Normal Senses and Modifiers, it says that to find the cost of a modifier on Vision, multiply enhancement percentage values by 1/5 to get the cost in character points. It also offers 1/10 for the cost of Hearing and Touch and 1/50 for the cost of taste/smell. This is suppose to be based on how Modifying Beings with One of Two Arms on p. B53, but the math isn't adding up for me:

Modifying one arm is 1/10 x modifier value, which works out to be the cost of modifying an extra arm minus the cost of the extra arm - basically how much your arm is worth. Makes sense.

As far as I can tell, the cost of Not Blind is [50], Not Deaf and Not Numb are both [20], and Not No-Sense-Of-Taste/Smell (that needs a better name) is [5]. So to take the example from Enhanced Senses, Precise is worth +100% and Hearing is x1/10, so Precise Hearing, per ES, should be [10], but +100% applied to Not Deaf [20] is [40], minus the intrinsic [20] for already not being deaf gives Precise Hearing a cost of [20].

What is it I'm doing wrong? It looks like all of the multiples in ES are one half of what they should be. Why is that discount there?

[Sindri]

Here's whswhs's commentary on that.

Originally Posted by whswhs

Yes, they are. But I examined the matter closely. In the first place, the precedent for this sort of thing is the rules for Extra Arms, about applying a modifier to the arms you naturally have. If, say, you take Short for one arm, the -50% modifier becomes a -5-point disadvantage, which implies that having an arm is worth 10 points (10 x -50% = -5). But One Arm is a -20-point disadvantage, so buying it off costs 20 points, not 10. Therefore the base value of the arm is not required to be the negative of the disadvantage of not having it. And the same can be true of the base value of sight, hearing, and so on.

In the second place, the rules for Scanning Sense make a 240° arc a +75% enhancement and a 360° arc a +125% enhancement; and they explicitly compare them to Peripheral Vision and 360° Vision. But those traits cost 15 points and 25 points. This implies an underlying value for Visible Light Vision of 20 points (20 x +125% = 25, for example). I thought it was desirable for all the other enhanced versions of human eyesight one might take to use the same implied value, for consistency.

I don't recall the details of how I got the point values for hearing, chemical senses, or touch, but if the use of a point value that's not simply the negative of the disadvantage for not having the sense is allowable for sight, the most important human sense, I don't see why it shouldn't be allowable for the others.

I wondered how long it would take before somebody brought this one up!

If we wanted to say that the base value had to be the negative of the disadvantage, then we'd have to change the Basic Set rules for modifying one or two arms; and, for example, we'd either have to make 360° Vision cost 62.5 points (Blindness is -50, and 50 x +125% = 62.5) or make Extended Arc, 360° a +50% enhancement (50 x +50% = 25). But either of those would change the RAW; my treatment does not.

[GodBeastX]

You are doing your math wrong. Extra Arm is 10 points. One arm is -20 points.

See a problem here?

Just go with the values they recommend.

Edit: Someone beat me to it.

[whswhs]

Originally Posted by GodBeastX

Edit: Someone beat me to it.

I did that whole analysis when I wrote Enhanced Senses, and then I had to persuade Kromm that it made sense, too. . . .

[Humabout]

Originally Posted by Sindri

Here's whswhs's commentary on that.

Thanks, that clears it up a bit. My head was hurting from looking at that!

Originally Posted by whswhs

I did that whole analysis when I wrote Enhanced Senses, and then I had to persuade Kromm that it made sense, too. . . .

That makes me feel a bit better. I can buy your solution now that I see it spelled out. I don't like taking things on faith, since I can't apply those things elsewhere afterward.