From: fortunati.luigi@gmail.com   
      
   Twin A is at the base of the tower where the watch  of twin B goes   
   slower than that at the top.   
      
   Is the distance AB in the reference of the twin A greater, less or   
   equal to the same distance measured in the reference of the twin B?   
      
   Second question: if there is a light signal that goes from A to B and   
   back reflecting on 2 mirrors placed in A and B, the round-trip time   
   (from A to B and from B to A) measured by the clock of the twin A is   
   greater, less or equal to the time measured by B for the path from B to   
   A and from A to B?   
      
   [[Mod. note --   
   Your first question is not precise enough to have a unique answer,   
   because "the distance AB" is not a uniquely defined concept in a   
   curved spacetime.  That is, there are a number of different possible   
   ways one might measure "the distance AB", such as:   
   (a) laying out meter sticks along a straight (vertical) line between   
       A and B, or   
   (b) doing angular surveying (trigonometry) via a short horizontal   
       baseline located at A, or   
   (c) doing angular surveying (trigonometry) via a short horizontal   
       baseline located at B, or   
   (d) measuring the round-trip light (or radar) travel time from   
       A to B and back to A via a clock which stays at A (as in your   
       second question), or   
   (e) measuring the round-trip light (or radar) travel time from   
       B to A and back to B via a clock which stays at B (as in your   
       second question).   
   In general (a), (b), (c), (d), and (e) will all give slightly   
   different answers, so you'll need to specify which of them (or   
   which other measurement procedure) you're asking about in order   
   for your question to be well-defined.   
      
   Your second question (basically asking if measurements (d) and (e)   
   above give different answers) does have a well-defined answer:   
   they're different.  The observer at the bottom of the tower (A)   
   measures a shorter time (faster "ticking rate") on her local clock   
   than the observer at the top of the tower (B) measures on her local   
   clock.   
      
   The difference you ask about in your second question is in fact   
   experimentally measurable with GPS satellites.  These broadcast a   
   signal which (simplifying a bit) is modulated at 10.22999999543 MHz   
   as measured by the satellites' on-board atomic clocks.  As received   
   on Earth, the signal is (found to be) modulated at (the faster rate)   
   10.23 MHz as measured by Earth-surface atomic clocks.  See   
     https://link.springer.com/article/10.12942/lrr-2003-1#Sec5   
   (particularly figure 2 and the text immediately following it) for   
   details.   
   -- jt]]   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)