There are now a number of survey sets for the entrance series.  Arguably the most accurate is the one lead by 
Willie Stanton in the early 1970's using a tripod mounted compass, with recorded precision of 10-seconds of arc.

The MCG Paper survey is described in the MCG Publication (number ?).  The author (Ben Cooper) scanned this electronically in 2006 to 
generate the origial electronic survey upon which the current electronic survey is based.  While some sections of the original 
survey are of high standard, the translation of this into an electronic three-dimensional survey was at best crude.  Clinometer 
data in particular has only been estimated based on a uniform slope from the entrance to the Red Room!  An approximate centre-line was
reverse engineered from the survey station markers visible in the drawing.  Later versions of the software Therion would have made this 
much simpler, obviating the need to reverse engineer a centreline and using the drawing directly in a scaled scrap.  

Most probblematic has been the accurate attachement of separate surveys onto the original paper survey.  No fixed point
survey stations were recorded in the available survey information, and hence continuation of the survey from the Canal has been 
approximate (within about 1m).  

Subsequent to scanning in the paper survey, other surveys of the Entrance series have come to light.  These are, in order of receipt

1. the 2000 survey of Midnight Passage by Ben Cooper and Paul Craddy
2. the 2007 re-survey of the Entrance by Martin and Yvonne Rowe, sadly stopped before completion due to Martin's health.
3. the 1986 survey from Tony Knibbs
4. the c. 1972 survey from Willie Stanton

These surveys are all brought together in this folder.  Similar survey stations appear within surveys at tight bends, and these
have been used to join the surveys together.  As stated before, this is likely to fix the surveys together to within about 1m of 
true.  While not perfect, it is sufficient to compare them.  By fixing at the first bend in the Entrance, any divergence is amplified
at the Midnight Chamber end of the survey.  Note that the WS data of 1972 appears to suggest that the entrance pipe was not yet in place.
This fact should be easily confirmed from the MCG publications.  

Subject to checking survey dates and hence declination values, the WS and TK surveys demonstrate superb corelation along their entire 
lengths.  The MYR survey shows a significant rotation to the South, which may be either a declination (date) error or a systemic error 
in the data set.  MYR used compass and clino, which usually gives increasing accuracy with number of recorded stations, so this result
is disappointing.