I copied this from my ED-21 Manual. It seems to contradict itself.
Helpful Hints On Blade Tension
Determining correct blade tension is somewhat subjective. It is learned through experience and is somewhat dependent on personal preference. A properly tensioned blade will last longer and be much less likely to break prematurely. If the blade tension is too loose, you will notice that the blade will tend to drift or slip offline when cutting, and you may also experience excessive vibration or unusual noise. A blade that is too tight will break prematurely.
Assuming the blade has been properly installed in the blade mounts when the blade tension lever is pushed fully back towards the rear of the saw, the blade should be properly tensioned. Test the blade tension by lightly plucking on the blade, like you would a guitar string, with your finger. If the blade is tight and tensioned correctly, you will get a clear and even note. If so, you are ready to proceed to operating and cutting with the saw. If not, for some cases after double checking that the blade is properly installed in the blade mounts, further blade tension fine tuning can be made by adjusting the rear knob to raise the upper arm slightly. Note: this is not the main function of the adjustment knob (see the following paragraph) and using this knob as the primary blade tensioner will cause premature wear and damage to the machine.
This saw has an adjustment knob K in the rear that can raise the blade mount up to 1” (25 mm). This allows you to fine-tune blade tension when needed, as well as to reposition the saw blade at a point where you can use a different part of the blade in the cutting area. This also allows you to use a piece of band saw blade, cut to a length of 5”- 6” (127-150 mm) in your saw, and gives you up to 3 inch cutting capacity when needed.Note: Do not over tension the knob as this can cause premature wear and damage to the machine.