A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: David Iwancio
Date: 2020 Oct 14, 00:05 -0700
Ensure you are keeping the reflection at or near the center of the pan, and/or consider a broader pan.
The goal is to use a reflection from a "free surface" that's only being affected by gravity. Get too close to the edges and deformations in the surface due to surface tension becomes signifigant.
It might also help to wait a bit longer for more of the oil to settle down into the bottom of the pan, giving gravity enough time to pull the oil off the sides (motor oil is designed to be viscuous, after all). Another idea might be to immerse the oil bottle into a warm water bath to heat it up (and reduce its viscocity) before you pour it into the pan.