Just an idea for fixing bad batches. Ive been working on a concept to see if it would work.
Say you make something and your recipe has too much of an ingredient by design. You would be able to hit a button that would be something like change previous batch. you could then adjust your ratios and enter how much of the previous batch you still have. It would update to tell you how much you would have to add to adjust the previous batch to meet the new ratios. I wish I could explain it better. LOL
It makes sense. Typically I just take notes. Notes are your best friend. I start lower on the flavors. And then out of a 15 ml bottle I’ll vape 5mls. If I decide to touch up an ingredient I just put the bottle on the scale and just add “x” amount of flavoring. So if I added 0.07grams of caramel I just add 0.07+ (Insert math ratios) to the recipie.
Once you’ve done this a few times you get very good at the math on the fly. No need for calculators because you see the ratios all the time. But this process is sooooo much easier when you mix by weight imo
At some point I’ll implement a way to adjust all flavors, keeping the proportions… Say you have a recipe with 3 flavors at 1% each - if you adjust it to 0.8% all 3 will be 0.8% - doesn’t sound useful, but when you have lots of flavors with % all over the place, it becomes handy 
With high to max VG recipes using PG base flavouring may cause the “Something is wrong with the numbers. PG/VG ratio?” warning if you are increasing the flavour.
Using VG flavouring this warning would not happen but most flavouring are PG base.
That’s what I think, please correct me if I’m wrong.
Correct - If your desired PG/VG-ratio is 10/90 then 11% flavoring would force it to be 11/89, giving you this error. Checking off “Max VG” removes this error 
I make all my juices at 30PG / 70VG I don’t think I would notice a ± 5% change in PG/VG but others might especially if it is a complexed recipe with more than 10 flavours where the change in ratio might be even higher than 10%.
I think it would be easier to just make another 5-15ml bottle. using custard as an example, if you steep for 3 weeks and it’s not quite right adding more flavours would mean steeping for another 2 weeks for the added flavour to blend in so you might as well make a new batch keeping to your original PG/VG ratio.