Measuring the size of the Earth

The software AVFORM

In internet we found this very interesting page and we used it to verify our calculation: Aviation Formulary By Ed Williams.
There you can also download an Excel spreadsheet AVFORM than contains a large number of formulas useful for navigation.

We have used two spreadsheet in particular:

GREAT CIRCLE: to measure the distance between two locations give Latitude and Longitude.
We used this spreadsheet to measure the actual distance of 43 km between the Boat Yard and the Beach Hut.

SUN: to calculate the local midday at a specific location in a particular day of the year.
We used this spreadsheet to calculate the local midday at the Boat Yard.
We had to modify the spreadsheet slightly, because the original version gives only the time of sunrise and sunset.
Therefore we added the formula "C10+(E10-C10)/2" in the cell J10, to calculate the local midday as an average between the times of sunrise and sunset.