Description and Notes:
As mentioned in Drawing Instruments, 1580-1980, p. 70, this type of quick-setting compass was originally developed by both Haff and Riefler at around 1960. But this particular set (PT-22) is still in production at present, as shown in the official Haff web site. Nevertheless the lining inside the box of this set is in different color of the ones still in production (i.e. crimson vs blue). Therefore it is believed that this set may either be produced earlier or be of higher quality as their Precision- Special (PS) series, since the color of the lining of which is also crimson.
The so called quick-setting action of the compass is achieved by first pulling down the screw knob located on the right arm, then the compass will be automatically opened by the force of the upper bow spring. The opening will be locked by the curved rack as soon as the pulling force on the screw knob is released, as the knob will be pulled up by an internal linear spring to engage the rack. The opening angle can then be micro adjusted by turning the knob either forward or backward. The compass can be closed by simply press the arms.