Learn Spanish (Latin America): Pon la perilla aquí por si necesitamos alinear los símbolos. - Put the knob here just in case we need to align the symbols.

You are right that 'just in case' expresses a hypothetical situation. However, the phrase por si behaves just like the trigger a lo mejor from this lesson: it is an exception that exclusively triggers the indicative when talking about a present or future possibility. That is why we use necesitamos instead of the subjunctive. If you used a different phrase like en caso de que, you would need the subjunctive (en caso de que necesitemos).

What exactly is a perilla?

A perilla is a small knob that you twist or turn. In Latin America, you will hear it used for things like the volume dial on a radio, the knob on a stove, or a round doorknob.

Why is alinear in the infinitive here?

When two verbs are used back-to-back and share the same subject (we need, and we are the ones doing the aligning), the second verb stays in its infinitive form. The verb necesitar connects directly to the infinitive without needing any prepositions like a or de in between.

Is pon an irregular command form?