Calendar - Glitchfiend/SereneSeasons GitHub Wiki

The Calendar is used to display the current season (Temperate or Tropical season depending on the biome), as well as how far along in the season it is. 1 filled row is Early, 2 is Mid, and all 3 is Late.

You can also check the tooltip by hovering over the Calendar in your inventory to see the exact sub-season, as well as how many days into the sub-season you are. The current tropical season/progression will also appear in parentheses.

The Calendar is also used in the crafting recipe for the Season Sensor.