I teach a modified f-stop method to find base exposure. We don't have f/stop timers but a chart is posted. I resisted teaching the technique as the enlarger optics were 3 element with poor performance wide open. However, the f/stop method was easier for students to find the basic exposure. After I changed how I taught exposure I replaced 3 element Belar lenses with improved Nikkor glass. You make do with what you got in a community DR.