During runup I noticed the amps went from +3 to -4 at around 1500 rpm on the way to 1900 for the runup. It went back to +3 again and stabilized there. Later in the flight I was checking the engine page and saw this happen again. Did not see it again later in the 2.5 hour flight but not sure why it's going negative like this.

Any ideas or is this normal?