The best applications for getting sharp detail are vector applications like Adobe Illustrator or Corel Draw. All the graphic components are mathematically derived so you can rotate lines and letters with absolute clarity. The problem with bitmap applications like Adobe Photoshop and Corel Photopaint is that when you rotate lines and letters, anti-aliasing is used which results in blurry edges. It could be that your old dials are blurry anyway!
I quickly googled "vector graphics freeware" and the first on the list is Inkscape
. A review link also lists DrawPlus. Vector graphics are quite difficult to learn. If you want to play with bitmap graphics The Gimp
is the most versatile freeware editor. It's not that easy to use either. The task needs an editor that can do layers (the lettering and dial graduations are separate objects over the background). You may find other applications by googling.