metwand

The last attempt to evade this salutary rule was that of James I., in the celebrated case of Evocation, when Coke stoutly replied to the monarch that he could only in such matters speak through his courts (per curiam), observing that the law was the golden metwand and measure to try the causes of subjects.

The Judicial Committee of the Privy Council 1909

But as to the second, arising from an unfitness not fixed by Nature, but superinduced by some positive acts, or arising from honorable motives, such as an occasional personal disability, of all things it ought to be defined by the fixed rule of law, what Lord Coke calls the golden metwand of the law, and not by the crooked cord of discretion.

The Works of the Right Honourable Edmund Burke, Vol. 07 (of 12) Edmund Burke 1763

A true tochstone, a sure metwand lieth before both their eyes.

The Scholemaster 1570

A true tochstone, a sure metwand lieth before both their eyes.

The Schoolmaster Roger Ascham 1541