Cutting Straight with a Handsaw

I needed to cut some boards I had salvaged for shelving, but my deep and abiding cheapness prevented me from buying a circular saw.  Instead, inspired by the limited tools series, I made a jig to make my hand saw more accurate.  This video shows such a jig:




In searching for a video with this type of low-tech jig, I discovered guides that use magnets -- and, wowie! Look at this one: