well my dear... a pass in O level is considered a minimum L1R4 less than 20 to get you into a polytechnic... because otherwise, you either go to private schools or retake of go to ITE..
you do the math and all the best for your O's!
The level of achievement in each subject is indicated by the grade obtained: A1 & A2 (Distinctions), B3 & B4 (Merit), C5 & C6 (Credit/Pass), D7 (Sub-Pass), E8 or F9, with A1 being the highest achievable grade and F9 the lowest.
http://library.thinkquest.org/05aug/01348/secondary.html