litljortindan wrote:litljortindan wrote:Surely in walking a chord length of 78.5km they will have deviated from a straight line by approximately

6371*(1-COS((ACOS((6371*6371*2-78.4*78.4)/(2*6371*6371))/2)))*1000 = 121m at the mid-point?

Or should that be (6371 - SQRT(6371*6371-POWER(6371*SIN(((78.5/40075)*2*PI())/2),2)))*1000 = 120m?

I noticed my error in taking the arc length of 78.5km as the chord length (which is actually 78.4km) so that should have been:

6371*(1-COS((ACOS((6371*6371*2-78.4*78.4)/(2*6371*6371))/2)))*1000 = 120.6m at the mid-point

or (6371 - SQRT(6371*6371-POWER(6371*SIN(((78.5/40075)*2*PI())/2),2)))*1000 = 120.3m