Seasonality measures the relative performance of calendar periods within a year. The measurement is typically calculated over multiple years. Seasonality shows which times of the year the item typically performs above/below average.
When calculating seasonality all the Time-Weighted Returns (TWR) for each calendar period over the specified number of years are calculated. For example, when calculating seasonality by month over 30 years, there will be 360 (12 * 30) monthly returns calculated. An average for each calendar period as well as an overall average are calculated. Seasonality can be calculated either normalized or not. Normalized Seasonality is the calendar period average divided by the overall average. Non-normalized Seasonality is just the calendar period average return. See the "Seasonality Values are Normalized" option in General Preferences - Other to choose whether seasonality values are calculated normalized or not.
The return values used in the calculation are based around 100. For example, a 5% TWR will be represented as 105, where a -5% TWR will be represented as 95.
Fund Manager can output the data points used in this calculation to a log file. By default the logging feature is turned off. To turn it on, create a new registry string value at:
HKEY_CURRENT_USER\Software\Beiley Software\Fund Manager\CurrentVersion\techanal
named "seasoniltylog" and set it to a value of "1". The log file is named "seasonilty_log.txt", and it will be located in your user's AppData\Roaming\Fund Manager folder (usually a hidden folder). This log file is appended when any seasonality calculation is performed, and deleted upon exiting Fund Manager.