How to Find the Right Gear for Interval Workouts

I've never tried to do like an interval workout like that on Erg mode but whenever I do 1515s or 3030s. Even though you start you're supposed to start counting at 15 or whatever, I feel like I always start a half a second before because you need to get up to speed when you were previously just ticking over at easy and so I'm curious if it's if it's actually goodIf you get that kind of like ramp up where all of a sudden it's gonna start increasing the the resistance for you instead of you having to click down a bunch of gears or whatever figure out exactly anyway.