In the Sencha 2 document for "First Desktop Application in Secha Architect 2"
this.getCarListings().down('#myChart').store.loadData(selections[0].data.quality);
giving null for store,
Insteade of it this.getCarListings().down('#chartPanel').down('#myChart').store.loadData(selections[0].data.quality);
As Parent panel contains a "chartPanel" and "chartPanel" contains a "myChart" grid panel: