Two aspects are used to give a level of certainty of the event coordinates, the source’s certainty and the researcher’s certainty, which we've attempted to reflect in the 'event reliability'. To allow a more understandable value, only the following numbers are used 100, 75, 50 and 25.
Certain (100%) – This is used when the event happened with a clearly referenced landmark in site. Mostly ports but also when the souce states ‘when we could see Monte Argentario’. or the master could see what he was referring to and was actually there or there abouts (i.e. not specifying a ‘distance from X’). So would also count ‘upon the formiche di grosseto’ (little outcrops of rock) as a certainty 100.
Essentially, 100 is given when the source is explicit and the source author could also be certain of the position.
High certainty (75%) – When the reference is to a feature too large to pin to a specific site, such as a bay, estuary, straights or something like that OR when the master gives an estimated distance from a fixed identifiable point. 100 miles from the Azores, 50 miles from Malta, the English channel.
Essentially, 75 when the source names a position explicitly but the source author could not be certain of exactly where or didn’t provide the information to pinpoint it.
Medium certainty (50%) – When the event location is not specified explicitly but can be securely inferred from contextual information by the researcher. E.g. the incident must have happened between Ismir and Zante (the two stops before and after the accident); or they put into Livorno the next day, ergo they must be no more than a day’s sailing from Livorno.
Therefore 50 when the source does not name an explicit position but we are fairly certain of the position regardless.
Uncertain (25%) – When there is genuine doubt on the part of the inputter as to the location. E.g. source says near ‘Cava delle Mele’. I don’t know where this is (maybe someone does?) There is a ‘Punta di Mele’ on Elba, which would also make sense in the context, but I am not sure enough. Therefore I enter the coordinates of Punta di Mele but it goes down as a 25.
So, 25 regardless of whether the source is explicit or not, for when we ourselves are not sure.