Although ScaleLine was fixed for v2.9, written 1 : X Scales are
still erroneous on some projections, for example Spherical Mercator.
OpenLayers Ticket #1890
The map in the centre has the wrong scale value (red).
The map on the right has the correct scale value (green).
This demo uses OpenLayers 'trunk' (/dev/) to allow for easier testing of potential solutions.