All this talk about the cutting angle, admittedly mainly by me, got me thinking. What about a digital angle finder (DAF)? A new 3/8 chain has a gullet of ~0.25" and a raker depth of 0.025", the resultant cutting angle should then be 5.7º Put short bar in vice and zero DAF, mark position on bar. Put chain on bar and locate at same position on bar where DAF was zeroed. This is a new chain that has had the cutters touched up but the rakers have never been touched, hence cutting angle is less than optimum. Here is one of my old square ground chains - note the poor profile of the left side raker nevertheless the angle is approaching optimum. Here is my well used ripping chain. With a 6.2º cutting angle the gullet is around 0.41" so the raker depth is around 0.044" Last time I used it this chain was cutting well. The DAF body appears to be made of some kind of Zn? alloy so it should be soft enough not to damage the cutter edge but I'm thinking of adding some sort of sacrificial angle in brass to protect the cutter a little more. When the piece of brass angle becomes too mangled I would just replace it. The DAF has to be held near vertical along the other axis but that could be achieved using a bubble level. While not perfect it appears to be easier than the caliper method especially as it is a direct measurement.