What did Anders Celsius base his standard for comparison on?

Anders Celsius based his temperature scale on the freezing and boiling points of water. He initially defined the scale with 0 degrees representing the boiling point of water and 100 degrees for the freezing point, but this was later reversed to the scale we use today, where 0 degrees is the freezing point and 100 degrees is the boiling point. This standardization was designed to provide a clear and practical way to measure temperature in scientific contexts.