By rule of thumb.

  There is an English 'idiom' - "By rule of thumb". This was presumably sanctioned by the English Church. It allowed a husband to chastise his wife, with a stick with a thickness, no bigger than that of the husband's thumb.

Comment by Geri,

Hi Philip. I think it is ascribed to ‘English Law’ but not particularly linked to a Church.

FROM GOOGLE 

1. The idiom conjures an image of someone being squashed under a gigantic thumb, as a bug may be squashed. The idiom to be under someone's thumb first appeared in the early eighteenth century, though why the thumb is the anatomy that is used in this phrase is unknown.

2.Rule of thumb

Meaning

A means of estimation made according to a rough and ready practical rule, not based on science or exact measurement.

Origin

This has been said to derive from the belief that English law allowed a man to beat his wife with a stick so long as it is was no thicker than his thumb. In 1782 Judge Sir Francis Buller is reported as having made this legal ruling. That same year James Gillray published a satirical cartoon attacking Buller and caricaturing him as 'Judge Thumb'.