IRC+10216 was again tracked through transit (from HST 19:13 to 20:30) with the s-curve correction effectively disabled (by setting SCURVE.AMP = 0). Unlike this time last night the correct version of the TCS was used this time :

A slight (2") step up through transit is seen in the elevation residuals (this is of the same size as the step seen in the transit inclinometry measured earlier in the day), but otherwise both azimuth and elevation residuals seem free of systematics. The raw rms's in (daz,del) are (1.1",1.1"), but note that immediately after the data were secured the humidity reached 98% and the dome was closed - so there must be some atmospheric contribution to these values.

It would seem that any effect at transit at this elevation is actually quite small, and that similar data (of 18 Mar and 18 Apr) utilizing the s-correction are perceptibly worse. The original concept that the transit step size diminishes with increasing elevation and/or the application (sign ?) of the s-correction may be incorrect !