For a book written over one hundred years ago, this writing is admirably clear and concise. Einstein explains moving beyond the limits of plane, Euclidian geometry (no pun intended). He certainly wasn’t saying Euclidian geometry was wrong per se, but rather that it wasn’t sufficient to deal with real practical problems of the world and space. If I have understood his work, time is not constant and the universe is spherical, or elliptical, in shape. If I can make a practical application of this masterly work, my weight as a semi-rigid body in a Galileian system will vary relative to the motion, i.e., acceleration or unaccelation, of my body in time-space and the point of observation. So, the next time my doctor complains about me being overweight, I can suggest that is due to the observation point and it is all relative anyway.