We received our certification letter today! In this case it is only for light metering. Light measurements can vary 1%-90% (or more!) even over a short distance. Also the angle the sensor is place at can have a dramatic effect on lighting values. We want to make sure the values we are reading are in accordance with ASTM Standards and can be scientifically verified should they be called into question.
Measure twice, cut once. It never hurts to double and triple check your measurements. While my Android phone from 2010 may not be certified, it can be calibrated to closely match our calibrated light meter. Triple checked with my more modern Samsung phone using the same Lux app.