You can't be absolutely sure unless you're using identical syringes... (What about the beakers - Are you sure they're absolutely identical?) I completely switched to syringes myself, I don't measure with pipettes anymore. Beakers (to me) are fine for relatively large mixtures. (Few hundred ml and such...)
About "Why always the same solution?": The (A) ammonium iron(III) citrate solution is quite different (in terms of specific gravity and surface tension) from the (B) potassium ferricyanide solution, and maybe this is causing you to always slightly err towards less for A, and more for B !??? At least that shows YOU are pretty consistent! Which is something good in my eyes...
Originally Posted by gandolfi