fix axis labels when x2 axis is used

pdb-js/src/app/y-axis-definition/y-axis-definition.component.html

@@ -1,6 +1,6 @@
 <div>
     <mat-form-field>
-      <mat-label>Y{{yIndex}}-Axis:</mat-label>
+      <mat-label>Y{{yIndex}}-Axis Scale:</mat-label>
       <mat-select [(value)]="yAxisScale">
         <mat-option value="LOG10">Logarithm</mat-option>
         <mat-option value="LINEAR">Linear</mat-option>
@@ -8,7 +8,7 @@
     </mat-form-field>
 
    <mat-form-field class="pdb-form-mid">
-    <mat-label>Y{{yIndex}}-Axis Range:</mat-label>
+    <mat-label>Y{{yIndex}}-Axis Unit:</mat-label>
     <mat-select [(value)]="yAxisUnit">
       <mat-optgroup label="⸺numbers⸺">
         <mat-option value="AUTOMATIC_NUMBER">auto (number)</mat-option>