The timezone sign convention is the same as the longitude sign convention: east is positive. The lat/long conventions are documented in ISO 6709, but they pred

The timezone sign convention is the same as the longitude sign convention: east is positive. The lat/long conventions are documented in ISO 6709, but they predate that standard, though I have not found a good history of it. Note that these sign conventions are not universal: for example, POSIX has the reverse sign on timezone offsets because west positive was more convenient for american unix developers. There are similar oddities for longitude.