http://www.fourmilab.ch/cship/timedial.html Gives a formula for time dialation which is repeated in many other soucres. In this version t'/to increases with v. Its time dilation time is meant to slow? http://www.phys.unsw.edu.au/einsteinlight/jw/module4_time_dilation.htm A useful set of pages for those wanting to learn. The derivation for time dilation is in the form I am familiar with as v increas t'/to decreases, time dilation I understand. Two different equations for the same thing cannot be right? I don't solve problems with SR, I have never needed to but still I try to undersand. Can someone help resolve this apparant problem.