The term Sketch From Memory is more understandable than Grade Something-or-Other. It does not require a separate explanation. When I started caving, I saw some maps with a survey grade and did not know what it was. When I learned that the grade indicated how the survey was done, I was disappointed. That could have been stated on the map in Plain English. Survey Grades have been a peeve of mine ever since. I argued to abolish grading at the meeting of the Survey Grades at the International Congress of Speleology in 2009.
There have been several slightly different definitions of Survey Grades: CRG 1950, CRG 1966, BCRA 1976, BCRA 2002, ASF, and UIS. If you give a grade, you should also state which definition. CRG 1966 and BCRA 1976 were defined in terms of accuracy. The specifications were given as plus-or-minus tolerances. I interpreted this to mean a uniform distribution as I would for a machined part, not a standard deviation. Nobody ever tried to show that their surveys actually met the accuracy standards. Instead they called every compass, tape, and clinometer survey Grade 5. The BCRA 2002 revisions made the specifications more closely match reality. In the furor after the change, I published an article with my thoughts about Specifying Survey Quality in Compass Points 31
http://www.chaos.org.uk/survex/cp/CP31/CP31.pdf .
I looked at closure errors from over 40 caves and gave a talk at the 2000 NSS Convention. I did not find any Grade 5 surveys and there were some near Grade 3.
Missouri has long had a tradition of excellent cave maps. Some of the early cave mappers were very good and later mappers matched their quality. Lang Brod once said there is no point in assigning a grade number if all the maps are the same grade (Missouri Speleology, Vol. IV, Nos. 1-2, p. 48).
Regarding significant digits: I started surveying writing station-to-floor and station-to-ceiling distances in my notes. I changed to station-to-floor and total passage height when I found I had some 53-foot high passages. No significant accuracy is gained by recording distances to the centimeter or inch/tenth foot. The larger angle errors determine the survey accuracy. The optimum length unit would be about 10 cm. However, I record the smaller units because they are numbered on the tape.