## Cross-calibration

The cross-calibration tool on this page was used in the construction of the SEPEM reference proton dataset. It can be applied to channels of data tables created by users.
### Table and channel selection

First select the data table to be used as a baseline for the calibration (table 1), and the data table which should be re-calibrated (table 2). When both tables have been selected, the page reloads with a selection of the data channels.
When the channels for tables 1 and 2 have been selected, press the `Run`

button to start the calculation of the calibration function.

The calibration procedure starts by building a list of epochs which coincide for both data tables. If there are no matching epochs, the process is aborted and a warning message is displayed. If at least two matching epochs are found, a linear regression is calculated of the form

*Y* = *a* + *b X* ,
where *X* represents channel 1 and *Y* represents channel 2. The actual cross-calibration is achieved by applying the inverse relation to channel 2.
### Results

The regression function is printed with the calculated regression coeffients and the number of matching data points. Four plots are shown as well:
- the original data on a linear scale, with the regression line and the bisector superimposed;
- the original data on a logarithmic scale, with the regression line and the bisector superimposed;
- the cross-calibrated data on a linear scale, with the original regression line and the bisector superimposed;
- the cross-calibrated data on a logarithmic scale, with the original regression line and the bisector superimposed;

If the current user is the creator of table 2 (the table to be cross-calibrated), the calibration relation can be applied to channel 2 by pressing the `Apply Calibration`

button (which is otherwise invisible). This action will update the data for channel 2 in the database.

**Caution:** This action is irreversible!

*Last modified on:* 3 October 2011.