In reply to G8ADD:
Being a meanie, I haven’t bought a Radio Communication Handbook since
the Sixth Edition
My copy is packed for moving house…
But the current RSGB yearbook has QSA as signal strength (but doesn’t mention QRK).
Wikipedia seems to agree with me http://en.wikipedia.org/wiki/Q_code
As does http://www.qsl.net/w5www/qcode.html although it uses “legibility” rather than “readability”. A couple of other refs I’ve checked seem to confirm it.