(Originais Teachy 2023) - Question Easy of English

In a small town, the local high school is organizing a science fair where students have to present experiments that involve both the principles of physics and the use of the English language. John, a senior student, is working on a project to demonstrate the relationship between the current passing through a conductor and the voltage applied to it. As part of his presentation, John needs to explain the steps of his experiment and the scientific concepts involved using proper English. Which modal verb should John use to express the necessity of following the experiment's steps in a precise order, considering the safety and accuracy of the results?