Strictly speaking, you weigh a tiny bit less when you are in the lobby of a massive skyscraper than you do at home. Why is this so?

Answer 1

In the lobby of a skyscraper,there is a lot of mass above you, at relatively close range. This exerts an upward gravitational force on you that opposes the downward gravitational pull of the Earth below.The net result is a lwer value of "g".

A pendulum clock would move slightly more slowly in that lobby, and gradually lose time.