Some sense can be made of the literature in astronomy using sites that give:
1) a = 5.5 light days = 1.4245 ten power 14 metres (Max Planck Institute for Extraterrestrial Physics).
2) a = 4.62 milliparsec = 1.426 ten power 14 metres (Nature Letters).
3) a = 840 AU = 1.257 ten power 14 metres (elementary astronomy course, site two using google “semimajor axis of S2,megaparsecs”.
The symbol mpc is used for milliparsecs and Mpc for megaparsecs. The astronomers never seem to have heard of the S. I system of units that is internationally agreed upon by everyone else. The Max Planck Institute for Extraterrestrial Physics uses 5.5 light days. I can already see that the Einstein theory is going to be wildly wrong, because delta phi using the above data is orders of magnitude greater than a degree or so per orbital interval. I will proceed to this simple calculation now.