"The length is one centimeter."
Translation:Το μήκος είναι ένα εκατοστό.
It's not wrong, but it probebly wasn't originally added, since εκατοστό is way more common in written and spoken Greek. I just added it, thank you. ^.^
My Greek builder friends always say πόντος : https://screenshots.firefox.com/RqxAUtOiCVbyPrBi/www.duolingo.com Incidentally I am off again Thursday to the Greek island for a fortnight - see you when I get back mid-March.