How do the buttons work on a Hotpoint First Edition Dishwasher?

I have recently inherited a Hotpoint First Edition dishwasher, but without the manual. There are three buttons on the panel :- The 'On' button (I've worked that one out!), a 65 degree and a 45 degree button.
How do I select a higher, or lower tempearture? What happens if they are both depressed?
I woiuld be grateful if any one could advise.