When I try to upgrade my armour to calibrated, it won't accept processed. It will accept standard, but it doesn't actually upgrade, it just loops forever using the same standard armour.

Tried this with MK2 and Mech

Seems to work fine for me with Modular armor. Have you set the recipe ingredient quality to processed?

Actually, I can't seem to upgrade anything to blue quality.... It just uses up the calibration matrix on normal items, and refuses to accept any green quality.

When you select the recipe for the Calibrator, you have to choose to use processed ingredients on the bottom of the screen. Have you done that?

No, I guess I just assumed it was "smart" ... But now I have to also improve the quality of the calibration matrix as well... This is the type of behaviour I was trying to avoid with the vanilla system :(

Okay so that was the issue all along, I just didn't understand how it worked. You can close/delete this.

Thank you for your time.

Unfortunately I don't know of any way to force the recipe quality of a crafting machine, or I would have done that.

If you don't want the to upgrade the calibration matrix you can enable "Allow multi-step upgrades" in the settings. Then you can upgrade standard -> calibrated using all standard ingredients.
Upgrading processed items with standard calibration matrices is not possible in the current approach. I think it could be done but would require a different implementation (using furnaces and the calibration matrix as "fuel").
You can also reduce the cost of upgrading upgrade items (calibration matrix, etc.) in the settings with "Upgrade item upgrade cost scale".

It isn't the cost at all that annoys me with the vanilla system, it's the 128 > 64 > 32 > 16 > approach that is tedious. Also the RNG where you have to break/remake your entire setup each time you add a new quality to siphon off the bits that get spit out at random quality.... (That's a game issue not your mod), it just feels annoying in general.

I realize you said you you don't know a way to force quality, I've never looked into making mods for this game, but is there a way for the machine to hold on to the item once it's upgraded to re-use it to upgrade it again? What about a machine that's 2 in 1 that hands an object to another half of itself to finish the process.

Anyways, thanks for the mod, have a wonderful day!

To clarify, I don't know how to force a machine to only accept inputs/recipes of a certain quality. But I CAN force a fixed output quality, which is how this mod is working, avoiding the vanilla RNG.

Such a machine should be possible using hidden proxy chests and inserters to put the output back into the input (or that of another part). Out of curiosity, what would your ideal quality system look like?

That is such a complicated question to answer as it would require a fix of the base game itself, and one I've answered many times before, but ... You asked! :D
My ideal quality idea is as follows:
Miners accept quality modules and output quality as it currently exists, this I didn't have much of an issue with.
ALL buildings can accept quality items regardless of the item being produced.
Example: Assembler is producing object A. It requires 20 items to make (10 steel, 5 green circuit, etc). If you're requesting to produce Rare(blue) quality, and you insert all blue, you get blue 100%... If you insert all standard objects, you get a 0.1% chance of getting a blue object, and a 1% of getting a green object. Each % quality adds to the outcome result, so if you insert 20 green quality objects, you have a 1% chance of getting a blue object.

(The numbers I provide are arbitrary, I'm sure someone who's much better at the maths could suggest a better calculation)

All items produced are of the quality requested (or lesser) never greater. If you ask to make a standard mech armor and use all legendary items, you sacrifice all legendary materials to get a standard result.

That takes care of my general overall idea... As far as upgrading materials to get a better result, I would introduce a precision manufacturer that can take x# of items, take the best materials from each, remove impurities, and pump out a new product as a result, but of higher quality, with a random (and guaranteed) chance to get a higher items, quality modules increase the chances of this outcome (I understand mods like this exist, but they're all very fixed and almost feel too cheaty, which is why I was interested in your mod as it requires actual effort and recipes to upgrade items).

As far as YOUR mod is concerned, I guess I assumed it worked sort of as follows

standard mech armor + post processing unit = processed mech armor
processed mech armor + housing = reinforced mech armor
This would be like upgrading a yellow inserter to make a blue, to make a green, etc. Each one uses the one before it, but with new items each time. Of course that isn't a quality upgrade but an item upgrade.

I've always hated the way quality worked in this game, it's by far my least favorite thing about Factorio.