diff -r f0ec83e1e01f -r dad62ec9af18 www/js/inv_fermentables.js
--- a/www/js/inv_fermentables.js	Wed Jan 23 22:36:31 2019 +0100
+++ b/www/js/inv_fermentables.js	Wed Jan 23 22:53:24 2019 +0100
@@ -43,6 +43,14 @@
 
 
 $(document).ready(function () {
+
+	var dataRecord = {};
+
+	function calcTotal(cost, inventory) {
+
+		$('#totval').val(cost * inventory);
+	}
+
 	var url = "includes/db_inventory_fermentables.php";
 	// prepare the data
 	var source = {
@@ -178,6 +186,9 @@
 	$("#production_date").jqxDateTimeInput( Dateopts );
 	$("#cost").jqxNumberInput( Spin2dec1 );
 	$("#tht_date").jqxDateTimeInput( Dateopts );
+	$("#totval").jqxNumberInput( Spin2dec1 );
+	$("#totval").jqxNumberInput({ width: 90, readOnly: true, spinButtons: false });
+
 	var dataAdapter = new $.jqx.dataAdapter(source);
 	var editrow = -1;
 	// initialize jqxGrid
@@ -263,7 +274,7 @@
 					editrow = row;
 					$("#popupWindow").jqxWindow({ position: { x: 110, y: 30 } });
 					// get the clicked row's data and initialize the input fields.
-					var dataRecord = $("#jqxgrid").jqxGrid('getrowdata', editrow);
+					dataRecord = $("#jqxgrid").jqxGrid('getrowdata', editrow);
 					$("#name").val(dataRecord.name);
 					$("#type").val(dataRecord.type);
 					$("#yield").val(dataRecord.yield);
@@ -288,12 +299,23 @@
 					$("#cost").val(dataRecord.cost);
 					$("#production_date").val(dataRecord.production_date);
 					$("#tht_date").val(dataRecord.tht_date);
+					calcTotal(dataRecord.cost, dataRecord.inventory);
 					// show the popup window.
 					$("#popupWindow").jqxWindow('open');
 				}
 			}
 		]
 	});
+
+	$("#cost").on('change', function (event) {
+		dataRecord.cost = parseFloat(event.args.value);
+		calcTotal(dataRecord.cost, dataRecord.inventory);
+	});
+	$("#inventory").on('change', function (event) {
+		dataRecord.inventory = parseFloat(event.args.value);
+		calcTotal(dataRecord.cost, dataRecord.inventory);
+	});
+
 	// initialize the popup window and buttons.
 	$("#popupWindow").jqxWindow({
 		width: 1050,