Home-made 4dKH solution

[magnosis]

I was reading Tom Barr's guide to making your own 4 dKH solution out of distilled water & baking soda, for use in a CO2 drop checker.

Other people in this thread have corrected Tom to use 6.0g of Baking Soda instead of 4.99.

I went with 6g, and this resulted in a solution that measured at 7 dKH with one test kit, and 9 dKH with another test kit.  Gurrh... now I don't even know what to trust....

Have you tried this method ?
Did you use 5g or 6g of baking soda ?
Did your KH test kit match the expectated 4 dKH ?

Are there different grades of Baking Soda, which would explain why Tom uses 5g, others use 6g, and I apparently need less than 5g ?

Lastly, where can I find (locally...) graduated cylinders (10ml, 50ml, 100ml, 1000ml) and other medical equipments ? I think there's a med supply store somewhere in Gatineau near the hospital but I couldn't find it with a quick drive-by yesterday...