Name:	Council Rock Doc -	Reply
Subject:	Water level Measurement
Date:	6/8/2015 12:27:02 PM

I am sure this subject has been explained previously, but what exactly is the difference between  490 ft Martin Datum and 491 MSL (Mean Sea Level)  and how are they calculated?  They seem to be one in the same, but evidently based upon differing starting points.

Thanks!

Name:	Osms -	Reply
Subject:	Water level Measurement
Date:	6/8/2015 4:48:28 PM

Martin Datum was the old way of measuring the water level and evidently the old way of measuring missed the real sea level by about one foot.  Therefore, while real sea level full pool level is 491' the old way of measuring said it was 490'.  Hey, 90 years ago, I'm surprised they got that close.  Think about surveyors having to figure that out, the old way.  All official, gubment stuff uses 491' mean sea level (msl).

Name:	Council Rock Doc -	Reply
Subject:	Water level Measurement
Date:	6/9/2015 10:22:39 AM

An even more astounding feat was that British surveyors, in the late 1800's, were able to calculate the height of Mt Everest and were only off 33 feet when compared to the known height today achieved with satellites and GPS calculation.  Thanks for the LM explanation!

Name:	Osms -	Reply
Subject:	Water level Measurement
Date:	6/9/2015 2:20:02 PM

I would have hated to carry the transit on that survey team!

Name:	au67 -	Reply
Subject:	Water level Measurement
Date:	6/10/2015 5:41:14 PM

Ya'll just remember that Eratosthenes determined that the circumference of the earth was 24,482 miles which is pretty close to the actual 24,901 miles.  This was in 240 BC and he never left home.

Name:	Summer Lover -	Reply
Subject:	Water level Measurement
Date:	6/11/2015 11:25:16 AM

I guess he just Googled it.  Wait a minute, AlGore had not been born yet....