Last time I voted a coupla months back in California, the poll worker wanted me to use their pen, and I told the guy that I was using my own pen. Interesting article: https://venturebeat.com/2020/11/01/optical-scanning-machines-are-susceptible-to-miscounting-u-s-voter-ballots/ Some pens are invisible to the scanner " machines were calibrated to read only carbon ink — not the dye-based ink found in many gel pens."