Datasets     HST start      mean leg temperatures   Humidity
                               start   middle   end       %
   inc990228      13:42         2.2     3.4     4.4      25
   inc990307      10:30         0.6     1.6     2.7      40

The difference between the model derived from the new data and the previous model of 990228 is shown below :

There is good agreement between the F1 and F2 terms, with rms scatters in the (F1,F2) differences of (0.50", 0.25"), but the F3 difference is highly structured in a way not seen before. The two largest features, at azimuths 244 and 292 occur at track joints :

- but how this ties in with the rest of the analysis below is unclear.
The good symmetry persists (see the plot ), but in assessing the symmetry we compare both TY and LY with RY, and the TY-vs-RY scatter is perfectly nominal (see the plot ).

The difference that has occurred is in the slope of the TY-vs-RY relationship :

The table below shows the slope of TY-vs-RY from recent data :

   Date(mmdd)  1109  1110  1111  1112  1114  1117  0107  0228  0307
   slope       0.82  0.80  0.86  0.84  0.82  0.80  0.81  0.83  0.66 
             +-0.01

An average over this ~4 month period prior to today would be 0.82 +- 0.01, and if needed I could produce similar numbers going back further in time, but my feeling is that the value 0.82 is representative of the previous history. A real and sudden change seems therefore to have occurred, seemingly in the coupling (scaling) between the motion of the right A-frame, as measured by RY, and that induced in the elevation axis, as measured by TY.

I have not installed the new track model, and await confirmatory data - hopefully on 990308.