There are several ways to pick eyepieces:
1) Even % jumps. Like Pentax XW or Morpheus progressions, this is usually a 40% jump up to the next...

I use combination of increase by factor (i.e. by 1.4x), exit pupil and U curve.

I star with 2mm exit pupil, where most of my galaxy hunting is done...

With the exception of my ES92s & Baader Morpheus ranges, I normally stay below 65° for FL <20mm. To have a FoV where its all visible, as for...

You might like this information, too:

The Erfles, and some other eyepieces are desribed by the Zeiss designers in

DIE FERNROHRE UND...

Enjoy Mr. Suiter book when you get to read it. :)

Star Testing Astronomical Telescopes: A Manual for Evaluation and Adjustment by Harold Richard...