I should have been more precise. What I really meant was that it can’t be going off just HV miles since mine indicated the first oil change at exactly 1 year and 1 day after purchase with <13 hours on the ICE and ~750 miles in HV. I installed an hour meter so the 13 hours includes the occasional brief ICE runs for assumed System Checks and starts due to reduced regen on a full battery. The miles were recorded on the 3 HV trips I made the first year and I never ran the battery down to 0 EV and had it automatically enter HV. I only drove ~7,600 miles the first year so that’s ~90% EV and 10% HV for me. Purchased 2/19/18; build date 11/17. MM later indicated “service due” on 2/12/18 at 7,442 miles. So I make the assumption that my low total miles allowed me to go the full year on the oil change since 750 miles/13 hours on the ICE is a ridiculously short oil change interval. It may have even timed out since it was at ~ 12 months. WBut we really don’t know what parameter(s) the MM is using since Honda is so tight lipped. All we know for sure is not to go over 1 year from the manual. It appears from the posts on this forum that with normal driving miles, most are seeing their MM call for 2 oil changes per year. And I don't begrudge my MM and the manual for having me change the oil at least once a year, even with my extremely low ICE usage, since oil does have its additives age and it accumulates moisture and acids that are best removed each year. I just wish Honda would tell us with what and how the MM is calculating all this. Not holding my breath.