"Out of the box, manual or lever type thermostats are off temperature by about 2-4 degrees. Due to the fact that they use a bi-metal to sense temperature, they will often let the temperature in the house slip by 2-4 degrees before telling the furnace to kick in! This leads to huge swing in temperature and lots of discomfort.
On the other hand, a digital thermostat comes out of the box 1/2 a degree to 1 degree off, has no mechanical parts to wear and instead of responding once the temperature drops 2-4 degrees; the newer models measure to a 1/100 of a degree.
Add to that 7 day programming and you can really make a huge improvement in your system comfort, control and energy efficiency!" -Bob T.