Calcs: Update diff percent to be a percent (#90533)

diff per unexpected results

packages/grafana-data/src/transformations/fieldReducer.test.ts

@@ -55,13 +55,14 @@ describe('Stats Calculators', () => {
   it('should calculate basic stats', () => {
     const stats = reduceField({
       field: basicTable.fields[0],
-      reducers: [ReducerID.first, ReducerID.last, ReducerID.mean, ReducerID.count],
+      reducers: [ReducerID.first, ReducerID.last, ReducerID.mean, ReducerID.count, ReducerID.diffperc],
     });
 
     expect(stats.first).toEqual(10);
     expect(stats.last).toEqual(20);
     expect(stats.mean).toEqual(15);
     expect(stats.count).toEqual(2);
+    expect(stats.diffperc).toEqual(100);
   });
 
   it('should handle undefined field data without crashing', () => {

packages/grafana-data/src/transformations/fieldReducer.ts

@@ -573,7 +573,7 @@ export function doStandardCalcs(field: Field, ignoreNulls: boolean, nullAsZero:
   }
 
   if (isNumber(calcs.firstNotNull) && isNumber(calcs.diff)) {
-    calcs.diffperc = calcs.diff / calcs.firstNotNull;
+    calcs.diffperc = (calcs.diff / calcs.firstNotNull) * 100;
   }
   return calcs;
 }