the scale that you ae refering to is called the heat anticipator. on old mercury tstats the system would always overshoot the stat setting, so they came up with an anticipator that corrects this. digital stats don't need this its built in. get your system checked by a pro. It should be checked every year by a pro. You change your oil on a regular basis don't you. A car is no different from a hvac unit. Ask your friends for a recommendation of a good repair company. We are not all crooks, but unfortunatly no-one ever gets to hear about the good ones.