Vibration exposure is measured in terms of acceleration. The measurement must be tri-axial and should be made according to power tool standard EN60745. The unit of acceleration is m/s². All power tools have a vibration value and once known, this value can be converted into trigger-time to allow the worker to calculate how long the tool should be used for. For example, the new Hitachi DH40MRY low vibration rotary hammer has a measured tri-axial vibration of 8.3 m/s². This tool can be continuously used for 2 hours and 54 minutes to reach the exposure limit value (ELV) of 5.0 m/s²(8) . Note this time is known as "trigger-time" and represents the total use time for the tool not including stoppages. You should add any stoppages to this time such as lunch breaks or non-tool work and preparation to calculate the maximum job time for using the tool. To see how to convert vibration to trigger-time, click here.