I would think that for legal purposes, marijuana would be treated the same as alcohol.
IIRC, with a full lab test, the levels or concentration of THC in your system can be determined and give a rough outline of the last time that or another drug was used. Dip tests are simple pass/fail and they are the norm because they are much cheaper.
That would be blood, not urine.
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Only blood-sample measurements are likely to correlate with a person's degree of exposure (3); attempts to correlate urine concentration with impairment or time of dose are complicated by variations in individual metabolism, metabolite accumulation in the chronic user, and urine volume changes due to diet, exercise, and age. Therefore, a positive result by the urine cannabinoid test indicates only the likelihood of prior use.
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