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If I remember correctly F=MA, which is how things are weighed on earth with a spring scale, or a balance for that matter. A calibrated spring is used to support an unknown mass at the surface of the earth. The spring compresses until the mass is motionless. The compression is measured and as the acceleration at the surface of the earth is known to be about 9.8 meters/ss the mass/earth weight is determined. All the the thought experiment illustrated was that gravitational acceleration and acceleration experienced in an accelerating reference frame are identical. If the reference frame acceleration is 9.8 meters/ss then the scale attached to the frame reads the same weight as when it is on the earth surface. Also an object released from a height of 4.9 meters from the earth surface or the floor of the box will take 1 second to hit the surface or floor. Strangely even in 1900 gravitational fields were described as acceleration fields, ie the gravitational attraction at the surface of the earth is 9.8 meters/ss. also acceleration due to gravity is easly calculated as : a = (ml*c^2)/R^2, where a= acceleration, ml= length of the gravitational mass, c= speed of light and R= the distance from the center of ml.
Tidal effects for a six foot person at the surface of the earth are at the feet 9.8000000 meters/ss and at the top of the head 9.7999944 meters/ss and may be ignored as we normally do when jaunting around this globe.

con morton