This replica is about half the size of a Portuguese Mariner's astrolabe. It was purchased in Portugal in 2014 and seems to be based on one of five recovered in 1971 from the wreck of the Spanish galleon Nuestra Senora de Atocha which went down in 1622 off Florida.
http://marinediscoveries.blogspot.com.au/2013/01/underwater-archeology-of-atocha.html
The 'Atocha III' astrolabe, which is now in the collection of the Museu de Marinhas in Lisbon, has an unusually shaped alidade with an apparent offset in each arm at the pinnule
http://nautarch.tamu.edu/shiplab/pw08astrolabes.htm
The pinnules were not reproduced in the replica as purchased, presumably because of casting problems, so these have been 'restored' in brass so that the astrolabe's method of use can be more easily appreciated.
