The machine is designed to accept timber of a common cross section but random lengths (practical minimum 1.8m) and, in a single pass, allocate a strength grade.

The operation  principle of the machine takes the proven  principle, that for all timbers,  there  is a  satisfactory working relationship between the stiffness and ultimate rupture strength, this relationship remaining true even when the timber is tested in the narrow section but used and loaded in the deep section.

During the single pass through the machine the timber is first measured for straightness in an unloaded condition at intervals of 152 mm.  This straightness measurement is then entered into a progressive memory whilst the timber proceeds to the loaded section of the machine and effectively travels with the piece being tested.

When the sample point arrives under the load roller, which exacts a precise load, the deflection      created by that load is measured.  From this measurement is subtracted the original straightness value, thus leaving a net value which is directly equitable to the stiffness of the piece.

This net value is then set in comparison with data (compiled by the appropriate authorities) to achieve one of five grades.  This procedure is repeated each 152 mm down the length of the timber and the    appropriate grade is allocated.  The process continued until the timber leaves the machine, when the lowest grade registered  (which has been stored in memory) will be marked automatically by the action of the roller marker.  Only grades 1 to 4 are marked  as grade 5 is reject.  At this time the board is fully tested and ancillary outputs signals are generated to action any supported mechanical handling.