function Scale(setting) {
    this._setting = setting || {};

    /**
     * Extent
     * @type {Array.<number>}
     * @protected
     */
    this._extent = [Infinity, -Infinity];

    /**
     * Step is calculated in adjustExtent
     * @type {Array.<number>}
     * @protected
     */
    this._interval = 0;

    this.init && this.init.apply(this, arguments);
}
@param {*} category
@return {number} The ordinal. If not found, return NaN.