The way the system works to determine each day's green, amber or red is by comparing each day to your moving average. There are also some other patterns of specific change that can trigger amber or red as well. Each day, there is a threshold for how far away from the average constitutes and amber vs. green vs. red based on standard deviation and in your case, obviously you were just one point away from being green on your reading.
The readiness score is a bit different in that it takes into account more than just a single day, it basically looks at the previous few days, placing more important of your readiness on the most recent days and less and less the more days you go back. Looking at your example, changing between an amber and a green on the current day obviously has the most significant effect on readiness score and given that in your HRV showed 2 amber, 1 red and 1 green, a 6 in that case is warranted because 3 out of the previous 4 days were not in the green.
In the second case where you changed it to green, then you had 2 straight days of green and 50% of your previous 4 days were green rather than just 25%. This is just how the system works, it doesn't mean there is a lot of "variability" in the system or scoring. You didn't score one point higher, you artificially changed the number to produce a different result.
In any formula there will always be thresholds that change the results and in a three color system, amber, green, and red, sometimes relatively small changes can cross the threshold to a different color, especially when there's a relatively small standard deviation, but when you just take the measurements and don't artificially change the results yourself, then it works exactly as it should.
It's true that I did manipulate the reading, but only because I was curious how the formula works.
The thing that I'm still wrapping my head around is that if my measurement were 74.9 this morning, I would have gotten a green indication and resulting readiness of 9, but if it were 74.8, I would get amber with resulting readiness of 6. That's one-tenth of a point affecting a training day decision. When considering how something as small as perhaps a stray thought can affect an HRV score, it feels like there ought to be more granularity.
Maybe the confusion stems from the idea of "readiness". To me, a readiness of 6 indicates I should reduce load significantly, whereas a readiness of 9 tells me I should work at higher intensity/volume. Intuitively it doesn't feel like there can be a 0.1 point difference between a 6 and a 9.
OK, I understand a lot better now. Thanks for taking the time to respond.
How can 1 HRV point change readiness by 3 points?
I love Bioforce HRV, I find it tremendously useful, recommend it to my friends who train, but this stuff drives me crazy.
Woke up this morning, took my reading. 74.5 which is pretty close to my average of late, so surprised to get an amber indication and a readiness of 6. I decide to see what would happen if I edited the record by one point, to make it 75.5. Now all of a sudden my readiness is green with a rating of 9!
Since we're not exposed to the math behind the readiness rating, I don't really know what to make of it; all I can speculate is that it's far too granular if 75.5 is "9 - all systems go!" and 74.5 is "6 - whoa there, reduce your training load by 30%". How am I actually supposed to use Bioforce HRV effectively when I know that readings themselves have so much variability?