Measurement Techniques and Tools
Using proper tools as well as correct measurement techniques are necessary to create PDDs that will be both accurate and useful. This section discusses the equipment you should have and the proper way to measure various aspects of tasks.
Tape Measure - Measure all heights, reaches and distances, associated with tasks.
Camera - Take pictures of each task as well as tools and working environment
Video Camera - Record the overall job for task identification, frequency, etc
Force Gauge - Measure push, pull forces
Note Pad - Take additional notes or observations
Scale - Weigh parts, tools and other objects
Stop Watch - Time task or cycle length
Clip Board - Hold paper or data collection sheets
Pen/Pencil - Record measurements and notes
Other Tools: - Dynamometer to estimate grip force 4 Pinch Force Gauge to estimate pinch force
How to Measure
Weight (part, tool, etc.) – Measured by either a scale or a force gauge, depending on the tool. A force gauge that includes a tension feature can be used to measure weight (NOTE: it is important that any chain, rope or hook that is used to hold the object is not included in the measured weight). If there is variation in the weight, multiple measures should be collected and averaged. It is recommended to report both the maximum weight measured and the average. Some items in a workplace may have a standardized weight that can simply be verified by measuring and recorded.
Force – Multiple measurements should be collected in order to ensure a representative measurement. It is recommended that at least 3, but more likely 5 or more, measurements be completed. The calculated average force should be used (note that there may be some judgment required to remove abnormally high or low measures compared to others that would otherwise skew the results). It is recommended to also document the maximum force measured.
Distance – A tape measure will be used to collect the distances for heights, reaches and distances.
Height – Must be measured as an absolute value. This is most typically measured from the floor height. Depending on the work environment, there may be other structures that height could be measured from such as platforms, staircases, etc.
Reach – Must be measured based on the work environment, not the individual. All reach distances must be measured from a physical barrier such as a table or railing.
Distance – Measured from start point to end point. This could be for walking, carrying, crawling, etc.
Frequency – Will be measured using a stop watch and/or a video camera. The number of times a task is completed will be counted. The number of tasks performed will be stated as a rate per minute, hour or shift. Video is the most accurate form of measurement because it can be reviewed after observation and verified. Note that cyclical jobs are most often stated as a rate per minute (e.g. 6/min).
Duration – The amount of time to perform a task should be measured using a stop watch and/ or a video camera. The duration of a task may vary and therefore may require averaging based on multiple measures of the task. Similar to frequency, video is the most accurate way to capture the duration of tasks.
Enviromental Factors to Document
There are many factors that can affect the physical demands of a task. It may be important to identify and document these types of factors in the PDD. Be sure to provide an appropriate amount of detail in order to understand why the environmental factor is important to the performance of the task.
How to Take Photographs
Significant effort should be made to take photographs of tasks that clearly illustrate the physical demands required. Photographs should be taken perpendicular to the work performed in order to capture the postures and technique used (either from directly behind, directly in front, or directly to the side of the worker). Photographs that are not taken from a 90 degree angle may be more difficult to visualize or understand the work being performed.
All photographs taken should include a clearly visible worker performing the desired task. If possible, the face of the worker should not be included, or at least blacked out or pixelated after the fact, to keep anonymity as much as possible.
Photographs should only include detail that is specific to the task. Visible backgrounds should be minimized to focus on the tasks itself. Unnecessary work environment details in the background of the photograph will reduce the focus on the task.