Function fit curve

Method estimates the moisture content of the filament. Dry the filament and measure the mass after same time interval.

Required hardware:

Scale (capacity: 2kg, resolution of 0.1g OR 4lbs, resolution of 0.003–0.005 oz).
Filament dryer
Timer, to remind you for the measuring

This tool fits a 4-parameter logistic (4PL) equation to the measured data points (see image 1).
Once the parameters of the function are known, it becomes possible to predict the drying behavior beyond the measured time range, even after the measurements have stopped.

4PL function

The parameter D represents the asymptotic value of the curve at infinite time, which corresponds to the theoretical perfectly dry mass of the filament.
Using this value, the moisture content of the filament can be calculated.

Moisture calculation

On next page, you can also enter a desired moisture level, and the tool will calculate the estimated time required to reach that moisture.

Important notice: the calculated moisture represents an average value for the entire filament (including the spool).
In reality, the outer layers of the filament will always dry faster than the inner layers. Therefore, when working with moisture-sensitive filaments, it is recommended to print directly from the filament dryer.

Enter the measured mass values in chronological order, one per line.
If a measurement was skipped (for example, you did not measure at that hour), you can leave the line empty or enter 0. Skipped points will be ignored in the fitting, but the time axis will remain correct.
The first measurement is required to calculate the initial moisture content. This first point is excluded from the curve fitting, because the system typically needs time to stabilize after heating starts.
You must provide at least 5 measured points in total. Since the first point is excluded from fitting, this leaves a minimum of 4 points for the curve fit.
More measurement points usually result in a more reliable fit.
It is recommended to continue the measurements until the mass change between consecutive time intervals becomes clearly smaller.
Any mass unit can be used, for example: grams (g), milligrams (mg), ounces (oz), or pounds (lb). The calculated results will be shown in the same unit you used for the input.

Time interval between measurements (hours)

Enter the time step between consecutive lines:
1 → measurements every 1 hour (recommended for longer drying)
0.5 → measurements every 30 minutes
0.25 → measurements every 15 minutes

If you find this tool useful, feel free to use it freely, free of charge.
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