function numDecimals(x) {
    x = x.toString();
    if (x.indexOf('.') > -1) {
      return x.length - x.indexOf('.') - 1;
    } else {
      return 0;
    }
  }
Specify a step value that dat.controllers.NumberController
increments by.

@param {Number} stepValue The step value for
dat.controllers.NumberController
@default if minimum and maximum specified increment is 1% of the
difference otherwise stepValue is 1
@returns {dat.controllers.NumberController} this