I would make my decision ASAP. I watched a recent program about recent changes in the Earth's core. I thought we were a dead planet by commercial break. Then they explained past similar phenomenon occured previous to the periodic reversal of the magnetic field. Our children's, children's, children will experience multiple poles and Northern Lights. Eventually the field will again stabilise with S as N and vis a vis. I miss everything <img src="images/graemlins/mad.gif" alt="" />. I concur with using a known system while teaching. Winging it makes one invariably look silly. Knowledge of multiple systems is fascinating, but redundancy less an issue than firemaking. Then again, I once got lost in a christmas tree lot <img src="images/graemlins/blush.gif" alt="" />. I hugged a Noble Fir until my nephew found me <img src="images/graemlins/grin.gif" alt="" />.