BangleApps/apps/calibration/boot.js

let cal_settings = require('Storage').readJSON("calibration.json", true) || {active: false};
Bangle.on('touch', function(button, xy) {
  // do nothing if the calibration is deactivated
  if (cal_settings.active === false || Bangle.disableCalibration) return;

  // reload the calibration offset at each touch event /!\ bad for the flash memory
  if (cal_settings.reload === true) {
    cal_settings = require('Storage').readJSON("calibration.json", true);
  }

  // apply the calibration offset
  xy.x = Math.round((xy.x + cal_settings.xoffset) * cal_settings.xscale);
  xy.y = Math.round((xy.y + cal_settings.yoffset) * cal_settings.yscale);
});