You practice breathing with this thing 4 times a day, ten breaths a session, and track the volume of your inhalations. In order to get the number to go up you need to take long, deep, and slow breaths.
It will give you a clear numerical result to track. 4 sessions a day, 10 breaths each, record your measurements, plug them into Excel, get an average going and work on driving it up.
I also feel like there's potentially a market for a digital incentive spirometer that could help people do these things. Especially if problems like this are somewhat common.
Pilates/yoga were good for core strength and stretching. If you want to start at home Yoga by Adriene on YT is very beginner friendly. I was never a fan of cardio or strength training but I did a bit of that too (it was a gym with various classes and instructors).
Also got a dog, it's a great excuse for daily walks.
One day I realised I was actually resting my head on the headrest in the car and wasn't uncomfortable. Until then it'd never felt right and made my throat feel tight at the front. I still have a way to go though, I have back issues and you don't fix 15 years of bad posture in 3 years.
Edit: I'll add after reading the other reply, at the start it's a struggle just knowing what good posture is. It doesn't feel right and natural, because your version of natural has been modified. You don't know how it's meant to feel. I found that exercises which exhaust certain muscle groups helped a lot. They gave up some of their grasp and let other muscles work. After a really heavy workout sometimes my back felt looser and more mobile and this helped me learn how it could feel.
Poor posture can be slowly changed and it is life changing, obviously worth it.
Surprisingly the tongue has some major effect on posture, especially on forward head posture. There are all sorts of tongue exercises that benefit breathing, posture and even the looks. Tongue should be basically resting behind top front teeth and slightly press up the palate. For exercises look up muscular imbalances and see if you identify any on your posture. But all things start at the feet though, if feet have a problem the whole chain up gets affected so pay attention to the whole body.
I wonder how accurate an app could get with movement detection if you lie down with your phone on your chest. Probably not very, but might be useful.
I bet there are interesting subtle dynamics beyond rate. Maybe interesting to record the acoustics inside the spirometer.
What's the product model? Prescription digital behavior change??
I imagine the digital version using a range finder at the top of the tube to calculate how high you raise the thing you're raising by breathing in and then calculate and report the volume of air you inhaled.
If you combine this with an app you've got a little product going. App can track progress over time. Show you some graphs. Remind you to use the spirometer.
Sell the digital spirometers to hospitals who sometimes give them to patients who have respiratory problems. Get some data to prove the digital version works better and then get insurance companies to cover it or buy it.
I want to try this. If you're happy with yours can you link to it? (everything I'm seeing is either under $10 or over $20 so I'm not sure which way to go)
As for being happy with it - yeah pretty much. It's not like it's mind blowing or anything and I've not tried any others to compare it to, so take that for what it's worth, but it works.
I keep mine next to my desk and use it when I'm bored or need a moment to think. I tried following the recommend pattern of use in the instructions but didn't stick to it for very long. Now I just use it when the fancy strikes me.