It's all natural.
  Conditions of the coating thickness could vary with your spinner, acceleration
speed and time, deceleration speed and time, and steady state spinning time and
age of your photoresist and room temperature of your lab and etc...........
  The good thing is you already know the recipe of your own. Company table is
just for the reference. Use your own.
  Good luck.

  sokwon

"Yu, Zeta (Tak For)"  wrote:
  Dear Fellows,

I am using AZ50. I got the data sheet relating film thickness and spin
speed. But the thickness I got is always significantly less than the
suggested values. E.g., 1250 rpm for 40 um (from curve: 55), 1000 rpm
for 50 (lately got 40 often) um (from curve: 65), and 750 rpm for 60 um
(from curve: 85). I got this PR recently and it is just manufactured,
and I use it when the PR warmed up to room temperature. If there is some
advice you can provide me? Thanks,