What steps do others out there take to ensure continued accuracy (past 12 months from new) of digital thermometers used to check hot and cold sentinel taps (legionella written scheme arrangements)? The engineer in me says that instruments should be calibrated at the points we are particularly interested in (20 and 50 degrees C), but also recognises that the response of these instruments is essentially linear at these lower temperatures, so one calibration point should do. Given this linearity, is it valid to suggest that 0 degrees is an equally reasonable calibration point ( very easy to do in-house with crushed ice bath). Casual enquiries made of the commercial food industry suggest they use the single point (0 degrees C) for devices used to monitor both fridges and cooked food......? A new battery every 12 months also seems sensible, but am I over-engineering the temperature calibration side of things here?