Please make the mouse-following line more obvious

[Reuben Thomas]

Thanks for this excellent app, which I've just (re?)discovered (who knows, I could have used it years ago and forgotten about it!).

The "follow mouse" line on the ruler often disappears into the ruler markings. It could usefully be made a bit bolder (it doesn't matter if it obscures the ruler markings, since the exact measurement is displayed on top of both) and also wider than the ruler. This helps the user to see that the correct position on the screen is being measured.