Use the lowest range that is larger than the pulse energy to be measured. For example, if you want to measure a 2.7 Joule pulse, use the 3 J range instead of the 30 J range. This will allow for maximum resolution (a 2.700 J reading versus a 2.70 J reading).
For most energy measurements, the default MEDIUM setting is appropriate. If taking measurements in a noisy environment or where there is a high level of background thermal radiation, the instrument may trigger spuriously on the noise or the background radiation. In this case, the user may select the HIGH threshold setting. This will prevent false triggering and ensure the sensor is measuring the intended pulse. If you are measuring small energies and the unit does not trigger, set the threshold for LOW. LOW threshold may also be used for the best accuracy if the energy measured is less than 10% of the range. For example if measuring less than .3 J in the 3 J range, LOW threshold is often more accurate, and will be more repeatable.