Some measuring devices go no lower than 0.1, others are more precise and can register as low as 0.04, etc. If you are being tested using one that goes no lower than 0.1, then that would be the lowest number that would show up.
For post-op patients, I have seen 0.1 as the threshold above which radiation or some other form of additional treatment is recommended.
Others may have seen different reports and if so, will share with you here.
Danman Bob, Born 1951
Nerve-sparing, open prostate surgery November 13, 2007
Gleason score 9, PSA 14; Biopsy result - 9 of 12 sticks showed cancer
Post-op pathology stated that cancer was confined to the prostate
Unrelated surgery January 2008 delayed incontinence recovery, which is now showing good signs of improvement (fraction of a pad a day as of late April 2008)
100 MG Viagra 3 times a week beginning December 2007
Osbon Erec-Aid Esteem manual pump for therapy beginning mid-February 2008
30 MG papaverine/1 MG phentolamine bimix injections beginning late April 2008
Five week post-op PSA 0.2, five month post-op PSA 0.1, next test August 2008