diff --git a/pdb-js/src/app/plot.service.ts b/pdb-js/src/app/plot.service.ts
index d2f7134..bd7cb03 100644
--- a/pdb-js/src/app/plot.service.ts
+++ b/pdb-js/src/app/plot.service.ts
@@ -128,20 +128,49 @@ export enum DataType {
 }
 
 export class AxesTypes {
-  x : Set<DataType>;
-  y : Set<DataType>;
+  x : Array<DataType>;
+  y : Array<DataType>;
   
-  constructor(x: Set<DataType>, y : Set<DataType>) {
+  constructor(x: Array<DataType>, y : Array<DataType>) {
     this.x = x;
     this.y = y;
   }
   
   hasXAxis(type : DataType){
-    return this.x.has(type);
+    return this.x.includes(type);
   }
   
   hasYAxis(type : DataType){
-    return this.y.has(type);
+    return this.y.includes(type);
+  }
+  
+  /**
+   * return the 1-indexed axis data type, e.g. getXAxisDataType(1) for the x1 axis 
+   */
+  getXAxisDataType(index: number){
+    if (this.x.length+1 >= index){
+      return this.x[index-1];
+    }
+    return undefined;
+  }
+  
+  /**
+   * return the 1-indexed axis data type, e.g. getYAxisDataType(1) for the x1 axis 
+   */
+  getYAxisDataType(index: number){
+    if (this.y.length+1 >= index){
+      return this.y[index-1];
+    }
+    return undefined;
+  }
+  
+  toString() {
+    const x1 = this.getXAxisDataType(1);
+    const y1 = this.getYAxisDataType(1);
+    const x2 = this.getXAxisDataType(2);
+    const y2 = this.getYAxisDataType(2);
+  
+    return "x1:"+DataType[x1]+ " y1:"+DataType[y1]+ " x2:"+DataType[x2]+ " y2:"+DataType[y2]; 
   }
 }
 
diff --git a/pdb-js/src/app/visualization-page/visualization-page.component.ts b/pdb-js/src/app/visualization-page/visualization-page.component.ts
index 9857897..7cd66ff 100644
--- a/pdb-js/src/app/visualization-page/visualization-page.component.ts
+++ b/pdb-js/src/app/visualization-page/visualization-page.component.ts
@@ -99,13 +99,17 @@ export class VisualizationPageComponent implements OnInit {
   
   getAxes() : AxesTypes {
     
-    var x = new Set<DataType>();
-    var y = new Set<DataType>();
+    var x = new Array<DataType>();
+    var y = new Array<DataType>();
     
     for(var i = 0; i < this.selectedPlotType.length; i++){
       var plotType = this.selectedPlotType[i];
-      x.add(plotType.xAxis);
-      y.add(plotType.yAxis);
+      if (!x.includes(plotType.xAxis)) {
+        x.push(plotType.xAxis);
+      }
+      if (!y.includes(plotType.yAxis)) {
+        y.push(plotType.yAxis);
+      }
     }
     
     return new AxesTypes(x,y);
@@ -233,6 +237,11 @@ export class DateRange {
   startDate: any;
   endDate: any;
   duration: any;
-      
-  
+}
+
+export class AxesUsed {
+  x1: DataType;
+  y1: DataType;
+  x2: DataType;
+  y2: DataType;
 }