First off, please excuse my ignorance on this topic. I am working on a project for a professor that involves georeferencing a historical map of Africa. It seemed easy enough until I realized my map was consistently 2.33 degrees off. Upon looking through the projections in ArcMap, I noticed that there was a projection called Voirol 1879 Paris. I also noticed that there are projections that use degrees and ones that use grads. I'm pretty sure that the map uses the Paris meridian, but I am unsure of how to tell if it is in grads or degrees. So I have three questions:
1. Is there a way to tell if the map is in grads or degrees?
2. Would I be able to reference it using the Voirol 1879 Paris projection and then transform it to a projection that uses the Greenwich meridian?
3. If it is possible, what would be the best way of accomplishing this?
I have attached the map in question. Any help would be greatly appreciated!