comprobabas
-you were checking
The word comprobabas is the imperfect form of comprobar in the second person singular. There are other translations for this conjugation.
See the full comprobar conjugation

comprobar

En los viejos tiempos, comprobabas el peso.
Old days, you check weight.
¿Por qué lo comprobabas?
Why were you checking?
¿Por qué lo comprobabas? Porque me lo pidió y David Lee no iba a hacerlo.
Why were you checking? Because he asked me to and David Lee wouldn't.
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