Thanks to you all for your replies - it seems the more I find out the less I know! This is why astrology is so endlessly fascinating and absorbing.
Cathy

I learned astrology with the Equal house system and have always used it. Having done some research it would seem that the Placidus system is more widely used outside of the UK. I've recently done a chart for someone using one with Equal then cast another with Placidus and there were some slight diff...