Layouts
While Butterworth's patent defined the relationship between the buttons, there have been a large number of layouts over the years, in terms of number of buttons, their range, and their spacings. Here are some examples I have found - more welcome!
From the 1896 Lachenal Tutor
The following four layouts are all taken from the tutor published in 1896 by Lachenal. The centre column of buttons is positioned slightly lower than normal (or were early models made like this?). Middle C has been circled.



A Crabb 80-key layout
This layout, used by Crabb up to the 1970s, was published by Geoff Crabb on concertina.net

Button size & spacing - Crabb v Lachenal
Geoff Crabb has kindly allowed the inclusion of this diagram, showing the relative button spacing and sizes on Crabb and Lachenal Crane duets.

Chord Chart
Based on the m-r-n-j chord notation in Brian Hayden's "Playing Chords" document, here is a chord chart for the 48-button Crane. Download the pdf document here.
