The commentary doubles as a synopsis and has therefore been reproduced in full:

To keep pace with the rising demand, more and more machines are needed in British mines that will load coal at the same time as cut it. Here at Plean colliery in Scotland, scraper boxes are doing both jobs in one.

Here's how a scraper box works. Fix a knife blade to a box, pull it along the coal face, and see how it peels off the coal. Hinge the back of the box to swing one way only, and the cut coal will be drawn along in one direction, but the box will ride over the coal on the back stroke. Put another knife in at the other end of the box, and the return stroke will cut coal as well. Now we have a tool that cuts coal both ways and loads it in one direction. Put several scraper boxes in the coal face and they will cut and shift coal from one to the other and so away to be loaded.

A 250 horsepower winch is used to drag the boxes up and down the face. At Plean, the control point is nearly half a mile from the face, but the operator can follow on his indicator the exact position of the boxes as they travel up and down along the coal. On the coal face, guide rails are used to keep the boxes pressed tight up against the coal. These guide rails are controlled by pneumatic pushers, and it's one man's job to keep the rails pushed in at the right place. As the knives on the scraper boxes cut more and more deeply under the coalface, the overhanging coal parts from the roof and falls to be collected by the boxes.

Behind the pusher operator come the prop setters. The roof here is so good that no bars are needed, and wedge props are simply set three feet apart. After the prop setters come the drawers-off. They clean up the spilled coal and then take down the back row of props as the face advances, leaving the roof to cave in behind them.

Here at Plean, 31 men have been averaging over 230 tons a shift, with a bigger output possible if they could get it away quickly enough. That's pretty good going, and the coal's not all small stuff either.