Tom, I dont understand. If you set up the scale, with the platforms and cups in place, at the total mix postitions, and zero it, and then you move the weight side in by the proper ratio, doesnt the mass balance itself out?

A higher mass of the arm would add to it's inertia, making it tend to accelerate slower and take longer to come to rest, but it shouldnt throw the accuracy off. Or am I missing something?

: Don, Paul has some excellent ideas. Thanks Paul. But I would suggest that you
: verify that the mass of the moment arm in you balance is not so great that
: it actually throws you mix off.

: As you move further out for your 2nd part of the mix, you are also adding
: that distance worth of mass to it from the arm itself.

: Mixing small batches will have a larger percentage of error.

: If the mass of the arm for the difference in distances is even 1/10 the mass
: of the smallest batch you plan on mixing, then you will have a 10% error.

: If the arm is light enough, then you should have no problems. Don't forget to
: include the mass of the platform for the water cup in its 2nd position as
: this is part of the arm and part of the error.

: Tom