Angel, the cat behind Halo, has four heart conditions and gets counted, weighed and medicated more than any cat should have to be. Her sister Yuumi has none of that. Yuumi's only instruction from the vet was to keep an eye on her weight before the next check-up. Different reasons entirely, but the same habit: write the number down and watch what it does over time.
Weight is the one thing almost every vet asks about
Whatever the appointment is for, most vets start by putting your pet on the scale. It's cheap, it's quick, and it says more than almost any other single measurement. A steady weight usually means things are ticking along. A number that moves, up or down, without an obvious reason, is often the first sign something is worth a closer look, in cats, dogs, rabbits, horses, and most animals a vet will see.
That's true whether your pet has a diagnosed condition or not. A vet doesn't need to suspect anything is wrong to ask you to track it. Sometimes it's simply "let's see where she is at the next visit."
The method changes with the animal
A change that means nothing on a large dog can matter a great deal on a guinea pig or a small cat, and a horse isn't weighed the way a cat is. Getting a number that's actually useful is less about owning the right scale and more about matching the method, and the units, to the animal you have. We go through this properly in Weighing a Great Dane vs a Guinea Pig, and if you're tracking a horse specifically, Tracking a Horse's Vital Signs covers what else is worth watching alongside weight.
Two cats, two completely different reasons
Angel takes several medications a day for her heart conditions, some cut in half, some given only twice a week, and her breathing rate gets counted regularly because a rising trend is an early warning sign for her specific conditions. None of that applies to Yuumi. She isn't unwell. She's a little overweight, and her vet wants her weight checked and written down before her next appointment, so they can see whether it's moving in the right direction.
Both of those are being tracked in the same app, on two separate profiles. That's really the point: a tracking app isn't only for a pet with a diagnosis. It's for anything a vet has asked you to keep an eye on, which covers a lot more pets than the ones who are actually sick.
Why a shared record matters with more than one pet
With two pets, or more, the complexity adds up fast. Angel needs a particular medication routine. Yuumi needs a particular diet. If either of them ever needs a cat sitter, or goes to the cattery, that's two different sets of instructions to get right, not one. Having both in one place, with one summary you can hand over or print, removes the chance of mixing them up when you're in a hurry.
Making it easy to keep track
Halo holds a separate profile for each pet, whatever they need tracking for, medication, weight, breathing rate or a daily log, and turns it into a one-page summary you can hand to anyone looking after them. It works the same whether your pet has four conditions or none at all.