function doConvert(methodName, ecModel, finder, value) {
	        var calendarModel = finder.calendarModel;
	        var seriesModel = finder.seriesModel;

	        var coordSys = calendarModel
	            ? calendarModel.coordinateSystem
	            : seriesModel
	            ? seriesModel.coordinateSystem
	            : null;

	        return coordSys === this ? coordSys[methodName](value) : null;
	    }
first day point of month
 @private