You tie it to something of a known mass and spin the pair.  The motion of these two bodies measures mass without the concept of gravity&#x2F;weight.  Or you throw it at something of known mass and measure the speed it imparts onto the known object.  Or you hang the known mass and the unknown mass on strings and measure the force of gravity between them, which may seem hard but can be done with stuff from Home Depo.<p><a href="https:&#x2F;&#x2F;www.fourmilab.ch&#x2F;gravitation&#x2F;foobar&#x2F;" rel="nofollow">https:&#x2F;&#x2F;www.fourmilab.ch&#x2F;gravitation&#x2F;foobar&#x2F;</a>