I've got a polygon featurelayer in ArcMap 10.
The coordinate system of the featurelayer's featureclass is web mercator.
The dataframe of the map uses an equal-area projected coordinate system.
I've got a field on the featureclass called Acreage.
I'd like to calculate Acreage based on the polygon's re-projected area (into that of the dataframe's projection). I don't want to create a new featureclass to do this.
Is there an easy way to do this in ArcMap 10?