Assuming that you mean a blade type, then the force that you need to be checking is on the end of the blade itself, not the torque of the bolt. You can do this best with a set of bathroom scales. With the blade clamped, push against the blade at the end. It should take around 60-65lbs (depending on manufacturer) to make it move. You then need to tighten or slacken the bolt in order to obtain the required pressure. This is actually quite awkward to do and helps if you park near a kerb or something that you can use to push against or else you can end up just pushing yourself backwards.
For more advise you can download a free .pdf document from the C & C Club web site. The bit that you need is on the last page under 'Stable Advice'.