This issue is closed as the official tool has been updated and most "algebric notation" pages look to be updated to use "-0 notation." Page kept as history and explanation of the notations.
Graticule longitudes and latitudes are indexes that look like relative integers. They are the minimal value of all the points in the graticule if the values are positive, and they are the maximal value of all the points in the graticule if the values are negative.
So (-23.452365°,16.415222°) is located in the Graticule -23,16.
And (23.452365°,-16.415222°) is located in the Graticule 23,-16.
With this notation, 0 and -0 are different values (this rule will be called "-0 notation").