I suggested using Sodium Carbonate to resolve the baking soda H2O and CO2 thing/issue.

I also have a lab verified reference sample at very high concentration, thus making shipping easier, as well as more accuracy when dilutions are done.
This provides higher confidence levels and it's easy, the solutions are pre made, all you do is dilute accurately with a flask with DI water.

The best test method would involve tritration pH meter end point and a digital tritrator like the HACH.

One thing is clear, test kits vary in this hobby, as do the dosing calculators for KH measurements. The range of accuracy is fairly wide and in most general cases, this is not an issue.

But we should all try hard to maintain a standard that's something we have confidence in. All these calculators have assumptions built into them.

You'll note Rnady and others do the chemistry and seldom rely on calculators. I am pre calculator in my area, so I do it the old fashion method as does Paul Sears or Randy at RC.

But for accurate critical measure of CO2, it is important.

For the drop checker method, having a lab verified reference solution that you can count on truly, is a nice option for a few $. I think it'll be about 10$+ shipping or so and 3.5 liters ought to last a few years and allow you to send all the KH ref solution you want to the friends etc

From there, a pH probe will be the thing that's the issue but ref solutions and their accuracy is easier to check for pH than KH.

I think this discussion is good as it outlines the issues with KH, it's measure, the web's various opposing measures/dosing calculators, different measurements etc, and methods available, test kit issues as well as a lab verified reference stock solution that is now available.

Before the myths start to amplify on the web, some definitive resolution should be made.

It seems that for lower Ref accuracy, the baking soda is fine.
For higher confidence/accuracy levels, go a lab grade vertified ref sample, they are relatively cheap, get a Volumetric flask((10$ or so for a 500ml) and you'll have plenty for years.

This will help understand and variation we see and give a new group of folks some back ground on the other types of alkalinity beside the carbonate type.

The system is more complex than some might assume on the Krib or various web sites.

And each step, going after such issues critically and in great detail, helps to provide a "closer to the truth" approach.

We may never arrive at the truth for most things, but we will know more about the issue and be better able to use it to help us in the hobby/life. I'd prefer that route versus mere belief
That choice is clear, at least to me.

Regards,
Tom Barr