as fig4 shows the four velocity bands selected experimentally in practice group reasonably well into two separate bands since the results for speed 1 and speed 2 lie close together and the results for speed 3 and speed 4 also lie close together it follows that for practical purposes the results could be grouped into two acoustic bands for kappa no 30 u2014 of these first and second bands the second gives a notably superior pulp yield at kappa number 30 it follows that in step 10 where the acoustic velocity through each unit of the batch of bulk wood units is measured if those units are to be processed to kappa number 30 then the operator should select for chemical pulping only those bulk wood units having an acoustic velocity greater than 3 km per second since these are the units which will yield the highest percentage of pulp when processed to kappa number 30 the bulk wood units having an acoustic velocity less than 3 km per second could be diverted to other uses e g mechanical pulping or could be used for chemical pulping in applications where an unbleached pulp is required however if the bulk wood units are to be processed to a higher kappa number e g a kappa number 40 then the operator might decide to lower the acoustic velocity cut off for selection to include the speed 2 group i e to select for chemical pulping bulk wood units which have an acoustic velocity greater than 2 7 km per second since the drop in pulp yield from the speed u00be groups to the speed 2 group at this higher kappa number is relatively small the reference scale of the type shown in fig4 also may be reworked for any specified kappa number.