In general, acceleration pickup has a main axis with which the acceleration sensitivity becomes its maximum. It is called "Sensing Axis" and align this axis with the desired measurement direction. Normally the sensing axis is close to perpendicular to the mounting base surface of the pickup.
With the pickup fixed to the vibration table and if it is vibrated in the direction of sensing axis, the pickup will provide rating output. Next, if the pickup is mounted on the vibration table with inclination angle θ for the sensing axis and vibrated, the output (SVθ) will be rating output multiplied by cosθ,　Output for the sensing axis will be SVθ*cosθ. If the θ is brought to 90 degrees, the output is supposed to become zero however, because of the existence of the Transverse Sensitivity (i.e. Sensitivity in any given direction perpendicular to the sensing axis), there will be some output. In the case of pickups offered by ACO, the lateral axis sensitivity is less than 5%.

Triple axis pickup is very useful since it can measure the vibration in 3 axis simultaneously. It is a convenient sensor to obtain composition of acceleration in 3 axes, or to measure and evaluate human body exposure to the vibration of machinery.
New product, 3 axis 10 mm X 10 mm, was developed in reply to the need to use the pickup at measurement site where only small mounting space is available. It contains preamplifier yet it is small and easy to connect.