you can not tell directly without a bow scale.
max out limb bolts (fully tightened) should put you close to 70lbs.
I suggest you back off both limb bolts 8 turns...exactly on each bolt from max tightness. review the video above by kenny parson. do not back off the bolts more than 13 turns or things will get exciting.
its best you use a super easy draw weight at first so you understand how it all works.
it also reduces the damage you can inflict accidently.
View attachment 5874185
from this table you can see roughly what poundage you can get
so setting C with 13 turns off the limb bolts equates to 47lbs
if you changed to grow with settings 41.75lbs and your draw length would be 28.5 inches
you can leave it on performance just turn it down on the limb bolts.. each turn on the bolts (one complete 360-degree turn) on performance setting will drop the poundage APPROX 1.75lbs ((70-47)/13=1.76923076923077)
so if you took off 8 turns that would be like turning it down 8*1.75=14. 70-14=56lbs so you would have a 55lb bow roughly.
if you lose track how many times you have turned down the bolts do them both back up to max and start again. you
MUST turn them down both equally or you get unequal tiller. what is tiller? read this
http://nockontv.com/article?download=44%3Atiller-tuning-and-holding-steady&start=40
hth