1692–1717, Robert South, Twelve Sermons Preached upon Several Occasions, 6th edition, volumes (please specify |volume=I to VI), London: […] J[ames] Bettenham, for Jonah Bowyer,[…], published 1727, →OCLC:
The foregoing doctrine affords us also a touchstone for the trial of spirits.
1950 January, Cecil J. Allen, “British Locomotive Practice and Performance”, in Railway Magazine, page 12:
"Expectation of life" is an elastic term: the touchstone here is rather the aggregate amount of work that the locomotive does during its working life.
2012, Ann Baynes Coiro, Thomas Fulton, Rethinking Historicism from Shakespeare to Milton, page 243:
In the print firestorm that followed the publication of the royal couple's letters, the generalissima was one polemical touchstone. The Annotations to The Kings Cabinet Opened itself depicted the queen as an enemy to king and country: […]