How do I know if my Simpson Contessa Dishwasher works?

I have a second hand Simpson Contessa Dishwasher that i am not sure if it is working to its capacity. i cant tell if the spray arms are rotating or the cycles are completing. There is a huge build up of lime and scale on the inside, so i have put the cleaner bottle in as instructed and began cycle on pot scrub. But i do not know if it is working to full capacity. I cant even tell by the noises that it is making (if any) as to what stage is up to. Please advise