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The angle of the scales which form the surface of the hair fiber, in radians. It affects the position of the highlight on the strand. This will typically be in the range of -0.05 to -0.1 radians for human hair (negative to tilt towards the root). Note that the final position is computed from this angle differently for each lobe so using the same value for all lobes will produce distinct highlights. Note that have different scale tilts per sampling lobe does't make geometric sense (the hair fiber doesn't change for each lobes) but this could be needed for artistic control.
A very basic OSL hair shader is presented below. Note that we use the same roughness in the longitudinal and azimuthal directions.
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