If your asking a question on vacuum pressure like this, you obviously dont have the knowledge or skill to synthesize LSD.
Here helpful links on pressure:
http://www.repairfaq.org/sam/lasercva.htm
Handy dandy vacuum chart*:
Inches of Hg Torr or
Rel to 1 atm Absolute mm of Hg PSI % Vacuum Microns
----------------------------------------------------------------------
0.0 29.92 760 14.696 0.0 -
0.40 29.52 750 14.5 1.3 -
10.24 19.68 500 9.7 34.0 -
18.11 11.81 300 5.8 61.0 -
25.98 3.94 100 1.93 87.0 -
27.95 1.97 50 0.97 93.5 -
28.92 1.00 25.4 0.4912 96.6 -
29.52 0.40 10.0 0.193 98.7 -
29.88 0.04 1.0 0.0193 99.9 1000.0
29.916 3.94*10-3 10-1 1.93*10-3 99.99 100.0
29.9196 3.94*10-4 10-2 1.93*10-4 99.999 10.0
29.91996 3.94*10-5 10-3 1.93*10-5 99.9999 1.0
29.919996 3.94*10-6 10-4 1.93*10-6 99.99999 0.1
29.9199996 3.94*10-7 10-5 1.93*10-7 99.999999 0.01
*=from source above.