General Mathematics · time series · manipulative

Reading a time series

Monthly sales over four years. Take each kind of movement out of the same data and see what is left — that is what naming trend, seasonality and irregular fluctuation means.

series trend line same month each year

The vertical scale is fixed, so switching a feature on or off changes the shape — never the zoom.

Build the series

Trend
long-term direction
+0.70
Seasonality
repeats every 12 months
16
Irregular
unsystematic month-to-month

Show

Trend line
the long-term direction alone
Season markers
the same month, year after year

Features present