Questions & Answers about Yo iba a medir la mezcla, pero lo olvidé.
Why use the imperfect tense for iba but the preterite for olvidé?
What does lo mean in lo olvidé if mezcla is feminine?
The pronoun lo doesn't refer to the feminine noun la mezcla. Instead, it acts as a neuter pronoun referring to the entire idea of "measuring the mixture." While in English we can simply say "I forgot," Spanish usually needs lo to represent the action or idea that was forgotten.
Could I use fui a medir instead of iba a medir?
Not if you want to express an unfulfilled plan. Iba a + infinitive means you intended to do something (but didn't). If you say fui a medir, it means you actually physically went somewhere and completed the action of measuring.
I usually hear people say se me olvidó. Can I use that here instead of lo olvidé?