That transparent over-guard is helpful when the power feeder need to be set close to the riving knife or machining non-through cuts on the table saw and actually in all cases the regular over blade guard get in the way. The power feeder, most of time bolted on the table, was a perfect holder and clearing the table to replace the tool is as simple as rotating the power feed unit.

A thing sheet of polycarbonate is fastened below the shaped wood base with brass screws. I added a pin to the power feeder and a threaded rod so that the guard could be locked and removed tool-free.

The guard can equally locks with either transparent face up or down as shown in the top photo. Whatever the arrangement the power feeder keeps its ability of driving the workpiece albeit the up position is more convenient as you may see below.

As instance, resawing does not allow the regular guard to be locked on the riving knife and the rear teeth throw much dust or thin chips which bite arms and face as hundredth of mosquitoes. The guard locks before the plate shield and channels nearly all dust downward.

The same vertical plate can hold the transparent angle in after position which is why the guard was originally designed. As you may see below I often use the table saw to machine non-through cuts or clearing mitring stick frames and the teeth tend to propel triangle offcuts backward as described in that paper about kickbacks. Moreover I most of time need to look at the workpiece which made me very uncomfortable and although any small stock had never hurt my body, fear was the best word to qualify my feeling. That see-through guard in such arrangement or as shown in the top photo locked on the power feeder fixed the issue.

Here are two less common uses amongst others of the angled over-guard.

Last but not least such guard needs to keep within reach and the rotating arm was designed to that purpose.