It's only desirability, weaker than ‘ought’ and ‘shall.’

The regulation reads, ‘a 2 x 2 inch guard rail should be installed at the extreme outer edge of these walkways', etc. (Italics added.) The question turns on the effect to be given to the word ‘should.’ One definition of that word is ‘Obligation in various degrees, usually milder than ought; as you should be obedient.’ Funk & Wagnall's New Standard Dictionary. As a reference to the cases cited in 39 Words and Phrases (Perm. ed.) 234 et seq., and Pocket Part 48, will illustrate, ‘should’ frequently implies a command, a duty or an obligation. But this is not always so. See *564 Nashville Ry. & Light Co. v. Lawson, 144 Tenn. 78, 98, 229 S.W. 741, 746; Godchaux v. Carpenter, 19 Nev. 415, 421, 14 P. 140, 142. Here, as in so many other instances, the meaning of the word and the intention to be ascribed to those who used it must be determined by the context. The provision in which it is found is one of several score safety regulations for the sawmill industry, most of which use ‘shall’, as, for example, 5.14(a), which immediately **843 precedes the provision in question and reads, ‘The vertical face of all green chains and sorting tables shall be boarded up to a height not less than eighteen (18) inches from the floor of the walkway.’ The occasional use of ‘should’ instead of ‘shall’ does not appear to be inadvertent but deliberate. Indeed, the entire code bears on its face evidence that it was prepared with great care and scrupulous regard to the right choice of language. We can only conclude that in those instances where departure is made from the mandatory ‘shall’ to the somewhat ambiguous ‘should’, the purpose was to express a different meaning—to convey the notion that the particular precaution was desirable and recommended, but not required. See, 3 Sutherland, Statutory Construction (3d ed.), 116, § 5821. In this view the regulation was not legally binding on the defendant and the instruction complained of was free from error.