Dynamically change the map spatial reference

[ab1]

Hi,
I have a map that uses ArcGIS Online in the small scales. So my map needs to be in Web Mercator in small scales.
In the big scales, my web client Flex application uses some feature and map services to do some area and distance calculations.
So my map needs absolutely to be in Lambert93, in the big scales, because geometric calculations in Web Mercator are not accurate at all.

=> I need to change the map spatial reference when I move from big/small scales to small/big scales. Is there a way to change the spatial reference of a map?

Regards.

[BjornSvensson]

In the big scales, my web client Flex application uses some feature and map services to do some area and distance calculations.  So my map needs absolutely to be in Lambert93, in the big scales, because geometric calculations in Web Mercator are not accurate at all.

The area and distance calculations are not dependent on the projection of the map.  Thus you don't need different projections at different scales for this.
http://resources.arcgis.com/en/help/flex-api/samples/index.html#/Clientside_Geodesic_calculations/01...
http://resources.arcgis.com/en/help/flex-api/samples/index.html#/Measure_lengths/01nq0000000n000000/