Cream of Tartar substitute?

I believe that your website is correct. my mother taught me that baking powder is equal to 1/4 baking soda & 5/8 cream of tartar the rest being made up of various other ingredients. Baking soda by itself is no good as it is alkaline and you need an acid so, depending on the recipe, you could try lemon juice, white vinegar or ermilk.