It's worth a look at the new BMC Belaying leaflet which takes into account the varying types of ropes and devices we now use. It's also worth familiarising yourself with the relevant terminology now recommended by the UIAA (e.g. Gri-gris are now 'assisted braking devices'). http://www.thebmc.co.uk/News.aspx?id=4332. To download a pdf of the leaflet click on the image above.