It's a fairly simple solution to make. The catch is that you need to be able to measure fairly accurately...
Mix 6 grams of sodium bicarb (Baking Soda) into 1 liter of distilled water. You'll have a liter of 200 dKH solution. Now all you have to do is dilute the solution. Take 10 milliliters of the 200 dKH solution and mix that with 490 milliliters of distilled water. This gives you 500 milliliters of your 4 dKH reference solution. Of course, you'll need the pH indicator solution (bromthymol blue...i believe) to make it all work. Add the 4 dKH solution to your drop checker and put in a couple drops of the blue pH indicator stuff.
I've never had issues with this recipe. However, the fact that I am exposed to a bio-chemical laboratory on a daily basis helps.
Good luck to you!
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Just because it's dirt doesn't make it low-tech.