Anybody understand length parameters of strand-based hair?

lamoid_5f20d3e469

I've been experimenting on and off for months, and I just cannot figure it out.  I'm going to list what I think is true about the length parameters:

1. Distribute tab: Density works as I expect, the larger the value, the more hair there is in any one region of skin. Width actually does specify the width of the hair in mm at the base and the hip. However, color, amount, and length have no effect whatsoever on the resulting render. They only affect what you see in the distribute tab.

2. Style tab. Scale curves and extend curves do affect the length of the hair. But it is unclear what the units are. mm? unitless scale factors? I don't think it is the former. But if the latter, where is the length specified that the scale multiplies?

3, Tweak tab: reduce length is opposite of what I would expect. Positive numbers reduce the length and negative numbers increase it. Again the units on the sliders seem to be meaningless apart from indicating more or less. Random length has no effect when the slider labelled length (max) is less than zero. [Why exactly are those values available then?] When it is positive the hairs get progressively shorter until they all disappear. So apparently the randomness is a random decrease only, even though the number is positive. No idea what the number means. mm? unitless scale factor? The probability distribution that controls the the randomness is a complete mystery, Uniform? Gaussian? Can't be that since there are no negative values.One-sided exponential?

4. This is not about length. But the shader is quite different from the usual ones, And as far as I can tell there is absolutely no documentation for it anywhere.

Just to be clear:  I really like this feature  -- strand-based hair, and I greatly appreciate that it is part of a free software package. But I sure would like to know what the various parameters mean or do.  

I would appreciate the comments or explanation of anybody who knows what the controls actually do.

Aside: wouldnt it be great if the folks that made these wonderfui programs (and they are wonderful!) actually provided explanations for how they work? Think of all the time that would save thier users. Manuals? In your dreams! That will never happen.