What is the most accurate area in body to take the temperate, we should (+) or (-) 0.5 ?

Rectal: Rectal is the most accurate, but not popular. It is usually not necessary either. You can take it orally with a digital thermometer or even on the forehead and temple, if you have a scanner. Scanners are very expensive and oral thermometers are under $10. You don't add or subtract from the reading that you get, just note how it was taken.