# Calculate Cottrell Equation

The **Calculate Cottrell Equation** command is used in current-vs.-tau^{–1/2} plots to determine the values of the parameters in the Cottrell equation for Chronoamperometry experiments. In order to use this command you must do a linear fit on the current-vs.-tau^{–1/2} plot.

## Method

Select the **Second Chart** tab to show the current-vs.-tau^{–1/2} plot.

Use the **Linear Fit** command to define a region of the plot.

Select the **Calculate Cottrell Equation** command from the document menu. The **Specify Linear Region to Fit** window appears.

Click the desired line, then click the **OK** button.

The **Cottrell Equation** window appears. Enter three of the four parameters of the Cottrell equation. The slope of the line with the user-entered parameters are used to determine the value for the one unknown, using the relationship that the slope = (*nFAD*^{1/2}*C*)/*π*^{1/2}.

Click the **Calculate** button.