Brief call with someone from HR, then another phone call with someone from the technical staff, followed by more in depth interviews with various people. This was mid-2020, so this was all on zoom. There were 6, one hour interviews, 3 on the first day and another 3 the next day. They asked about my experience and lots of questions about my approach to process engineering and problem solving in general. The CTO asked a few “test” type questions (how could you measure temperature in a particular process? How would you design a certain type of experiment?) that were pretty straightforward. I thought all the interviews went really well, so I was surprised I didn’t get an offer. They must’ve had someone else with more relevant experience.