I made that graphic before google earth and I used an internet azimuth calculator like this one to check the alignment:
the accuracy is maybe good to a mile or so, which is quite accurate for Egypt to England and the sites in between.
However, I have refined my calculations for the alignment of Giza, Ollantaytambo, Nazca and Easter Island, and the alignment is exact. Also, as described on my website:
Distance from Giza to Ollantaytambo = 30% of earth circumference
Distance from Giza to Nazca = 50% of circumference/phi
Distance from Giza to Easter Island = 25% of circumference x phi