bpm/tempo changes in loop - cant sync to exact matching bpm

hi all,

i am finding that i have deck 1 playing and on the deck 2 i change the tempo to match the playing track on deck 1.  when i slide the tempo slider, it usually catches at the bpm from the deck 1 playing track like it knows i am trying to match them exactly.  this is great!  then i will create a loop on deck 2 to prepare for the transition but i notice the bpm/tempo will change slightly.  i try sliding the tempo bar to match it up exactly w/ deck 1 again but i cannot seem to get it perfect, its always off by a few tenths (.10) of a beat.

anyone know why and how to avoid this?