The kiln opening

When Mara told me to judge the kiln by the colour inside rather than by the dial, I thought she was testing me. The numbers were clear; the shifting orange light seemed impossible to measure. I wrote down every reading, ready to prove that the instrument was safer than guesswork. Yet as the firing continued, the dial needle trembled while Mara’s description of a ‘bright apricot’ remained exact. By the time we closed the vents, I was waiting for her quiet verdict before I looked at the scale.

From the passage, select one word or phrase that shows the narrator’s initial doubt about Mara’s method and one word or phrase that shows the narrator’s growing trust in it.