How to get winform webbrowser zoom value?

As we know, we could set winform webbrowser zoom value by

var browserInst = ((SHDocVw.IWebBrowser2)(webbrowser.ActiveXInstance));
browserInst.ExecWB(SHDocVw.OLECMDID.OLECMDID_OPTICAL_ZOOM, SHDocVw.OLECMDEXECOPT.OLECMDEXECOPT_SHOWHELP,IntPtr.Zero, ref pvaIn);

or

webbrowser.Document.body.style

, the second way is not what i want. But we could only set zoom value by using the first way. So i want to ask for another to get the zoom value.