[jacquesm]

See the text in the article about the 'unspecified'.

As for the scale, it doesn't get much more precise than this, the only concession to legibility is to stretch the graph horizontally because otherwise it would be only 138 pixels wide, vertical is very close to one posting per pixel.

As the volume of postings on news.ycombinator increases due to increased traffic to the site the graph will stretch more further to the right.

This could be counteracted by changing the algorithm to 'bin' more posts to the right hand side to get for instance one month per bin, but in practice the outcome would be the same, you'd just have another weighting to do to get the Y-axis of the bins to line up.