What thickness is a 'hairline'?

I've posed this question before, many CDR levels ago, but the anomally still seems to exist even in X6.

When a line is drawn with 'hairline' thickness, CDR produces a line which has a thickness of around .075mm

This is easily verified by zooming in, especially if you draw an adjacent  line of say .001mm by comparison.  This of course presents an issue when working on fine small scale graphics, where the line has to be thinned to be visually useable.

What thickness should a hariline be then?  My feeling for what it's worth is that although a hairline needs to be visible to be useful, it should always present thinner than the thinnest line that can be drawn with a specific line weight.  A limitation to this may be that for technical reasons it cannot be represented thinner than the thinnest line available to be specified in Corel Draw (in metric, .001mm I think), but I would be surprised if this technical limitation exists anyway.

Any thoughts?