GPS question

[[AK]Clay]

Below is data that a friend collected while borrowing my GPS. We were wondering about the repeatability was of my GPS, but we got slowed down because we're not sure how many feet there are to a degree at our location in the world. I'm assuming that the N/S cooridinate is constant at 69.1722 miles/degree, but since we're north of the equator, and the earth isn't perfectly spherical, how do I find out how many feet per degree are there at my location?

-Clay


GPS data
Garmin E-treks GPS data @ a constant location

Location #1. Flag pole at RWL residence.
Date Time #Sat Claimed accuracy Elev N W
5/29/2004 6:30 7 20 1364 44.95749 89.33037
5/30/2004 8:15 5 19 1382 44.9575 89.33033
5/31/2004 8:30 8 17 1371 44.95751 89.33035
5/31/2004 20:08 5 28 1367 44.9575 89.33032
Average 1371 44.9575 89.3303425
Stndev 7.874007874 8.16678E-06 2.21614E-05



Location #2. RWL
Date Time #Sat Claimed accuracy Elev N W
5/25/2004 20:50 4 20 1461 44.95789 89.33093
5/26/2004 6:45 5 26 1369 44.958 89.331
5/26/2004 18:20 4 29 1438 44.95792 89.33085
5/27/2004 20:35 4 21 1413 44.95799 89.33093
5/29/2004 6:25 4 39 1380 44.95802 89.33097
5/30/2004 8:12 5 29 1438 44.95793 89.33089
5/31/2004 8:30 6 19 1385 44.958 89.33091
5/31/2004 20:05 5 20 1392 44.958 89.33094
Average 1409.5 44.95796875 89.3309275
Stndev 33.1791673 4.79473E-05 4.61945E-05

[[AK]Sonic Boom]

Diameter of the Earth at the Equator (7,926.41 miles)
Times Pi (3.14159) =
Circumference of the Earth (24901.53 miles)
Divided by 360 degrees = 69.17 miles
Times Feet per Mile (5280) = 365,222.44 feet/degree

Now wasn't that fun?