I’ve found with Tabata intervals, you don’t need to worry a ton about hitting an exact number but you do need to be ok with shutting it down if you don’t have the legs.
Tabatas are MAX intensity efforts. There’s no holding back. This kind of effort is short and intense which means you’re a lot better off going by feel than staring at your screen. If you crash and burn after 6 or 7, that’s fine, just stop there (at least, that’s what Izumi Tabata perscribed for his athletes, this plan may vary). If you’re not getting into zone6/ 7, you’re not getting the stimulus you need for this to be effective.
My personal favorite way to do Tabatas is with music made for Tabata intervals. Do a search for it and you’ll find a bunch of tracks. Typically there’s very quiet music during rest then really loud for the “on” portion. I like it because it allows me to just focus 100% on going all out. No looking at screens, no thinking, just give it everything when the music starts until it stops.