NavList:

Sorry if I was oblique with my refrence to EOT but looking at a modern table for March the EOT is negative.  Look at the data form - Cor. Eq. T  5 13.3 + A.T.  It seems to me that it shows M.T.G. = EOT + A.T.  So to get apperent time :

A.T. = M.T.G. - EOT

I saw the  + AT reference but was not sure if the "+" meant add to AT to get MT or the opposite. I tried both and  subtracting  gave me a sensible answer.

Here are my results

GPS   41° 17.57' S    174°  47.36' E

CoP app    41° 17.3' S   174°   48.0' E

Blackburne's Sumner    41° 18' 30" S  174° 46' 27"

These numbers tell me three things:

• The observations were accurate to <0.3'. This is to be expected given that they were taken on land by an experienced Extra Master who was Nautical Adviser to the NZ Government and also Examiner of Masters and Mates.
• There were errors in Blackburne's reduction method. This was acknowledged by Blackburne.
• The concept of a datum is meaningless when comparing observed  positions.

Thanks to John and Frank for pointing me in the correct direction. I plan to follow the links and download the 1902 NA. Then I can work the timesights from scratch using the sin² 1/2t  (hav) formula and tables.