I'm clear about the precision expressed by 0.5 implying between 0.45 and 0.55, just as 0.50 implies between 0.495 and 0.505. However, I don't understand why 1/2 inch means between 1/4 and 3/4. I don't think that it would be normal in the imperial system to specify a higher level of precision by stating a dimension as, say, 2/4", or perhaps 32/64". I studied engineering as the SI system was becoming the standard, partly, I thought, because it removed some of the many uncertainties in the former systems of units. If I order a 1/2", or indeed, a 5/16" bolt, I think I would need to refer to some sort of standards document or manufacturer's spec sheet to find out the relevant tolerances. I don't think it could be inferred from the description. Actually, I guess the same is true when specifying an M10 bolt - but perhaps that's why it is described as an M10 bolt, not a 10mm bolt...
And I'm not sure about Step Turn's runway 'E'. If a nautical helmsman was told to steer E, I think he would be in trouble if he went anywhere close to NE or SE. I think it would rather depend on the number of points marked on the compass. Which, of course, is not necessarily linked to the precision, or the accuracy, of the compass!