KCFly: One gram of NegativeMass(TM) will reduce the mass of the object it is glued to by one gram, i.e. it has a -1 gram mass, so the ratio is 1:1.

Technical Specs: As you know, relativistic mass increases as one approaches the speed of light. We have found that by moving certain objects with a negative velocity, they develop negative mass. I know what your thinking... we too had to fly our planes backward for awhile. Then my lab assistant had the bright idea of rotating the NegativeMass(TM) 180 degrees in the plane and PRESTO, we could fly forward again. Just be sure to observe the arrow stamped on the outside of the shipping container and you'll be OK.