I just left a note about procuring source materials on your talk page Also with reference to your mention of Cassini s tables you might like to notice that the practice about signs in the eighteenth century tables was to treat a sign as just a superior unit of 30 degrees this is shown by the presence of this unit also in the tables of increments corresponding to periods of time and in the tables of angular differences such as mean anomaly these usages show that such a sign did not need to begin at any particular place it was just any arc of 30 degrees a practice also mentioned as occasionally occurring in ancient times I think by O Neugebauer in History of Ancient Mathematical Astronomy