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Brad,
Interesting suggestion. There are no pictures of the HR1 cotangent scale in Ronald van Reit's paper although there is quite a good one of the MHR1. Gary Lapook has posted HR1 photos http://www.fer3.com/arc/m2.aspx?i=109378&y=200908 and http://www.fer3.com/arc/m2.aspx?i=111603 . There are no HR1 cotangent scale photos in the first group but there are 2 in the second and http://fer3.com/arc/img/111603.img_2189.jpg shows that the D mark is indeed missing between 70 and 71 degrees. There are also other features in this image that might be used compare to your MHR1 and lend support to your hypothesis. The F marks at 80d and 82d contact the degree symbol in the supplementary angle to the left. This doesn't appear to happen elsewhere.
With regards to the survey: not only is the amount of variation surprising but so too is the lack of consistency in the patterns used towards the two ends of the cotangent scale. The markings would be expected to be symmetric on either side of the midpoint (45 degrees). Your observation that marking G occurs only at 85d30' and 84d30' but not 4d30' and 5d30' is one example of this inconsistency. The introduction of marking G makes a certain amount of sense since the labels are only at 20' intervals in the range 84d to 86d,

Regards,
Robin
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