I have a square table that used to be perfectly stable, back when it had a foot at the end of each leg. Now the feet are missing from legs B, C, and D There's only one left at leg A.

The table measures 50 cm x 50 cm with legs 99.5 cm long. The foot is flat and attached by a swivel so that the end of leg A is a constant 0.5 cm from the ground. (In other words, the total length of leg A plus the foot is 100cm, 0.5 cm longer than each of the other three.)

The table can now rock back and forth with the foot of A and its opposite leg C in constant contact with the floor.

If B is also in contact with the floor, how far is D from the floor?

Note: consider the tips of the legs to be singular points at the corners of a square.