In reply to Seema's Q, in practice maximum A value is 3 while it may be possible to get more than this if you increase sensitivity of the instrument. See this image.
In reply to Mohd. Jahid's Q, Calorimetry and Coulometry (Coulo from Coulombs, unit of electric charge) are quite different. In the former, heat measurements are taken to analyse chemical reactions; while in the latter as well as in a related analytical method electrogravimetry, potentiometric measurement are made in the absence of external current flow. Purdue university's this classroom note explains coulometry very well. Also don't get confused with Colorimetry, measuring color as in spectrophotometer.