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# OnScale Method of the IZoomViewerEvents Interface

> OnScale method of the IZoomViewerEvents Interface in ABBYY FineReader Engine Visual Components on Windows — This method is implemented on the client-side.

This method is implemented on the client-side. It is called by ABBYY FineReader Engine before scaling an image in [Zoom Viewer](/fine-reader/engine/visual-components-reference/zoomviewer).

The method delivers to the client the scale value. With the help of this method it is possible to cancel the operation.

## Syntax

### C++

```cpp theme={null}
HRESULT OnScale(
  int           ScaleValue,
  VARIANT_BOOL* Cancel
);
```

### C\#

```csharp theme={null}
void OnScale(
  int      ScaleValue,
  out bool Cancel
);
```

### Visual Basic .NET

```vb theme={null}
Sub OnScale( _
  ScaleValue As Integer, _
  ByRef Cancel As Boolean _
)
```

## Parameters

ScaleValue

\[in] Contains the scale value in percentage points.

Cancel

\[out] You may set this variable to TRUE to indicate that the process should be terminated. In this case, the image will not be scaled.

## Return values

\[C++ only] If this method returns a value other than S\_OK, it indicates that an error occurred on the client-side, and in this case the value of the Cancel parameter is not taken into account.

## Remarks

The client implementation of this method must assure that all exceptions thrown inside the method are caught and handled and no exceptions are propagated outside the method. Propagation of an exception outside the method may lead to unpredictable results (such as program termination).

## See also

[IZoomViewerEvents](/fine-reader/engine/visual-components-reference/izoomviewerevents)