tim puko with "the wall street journal." thank you. hank you. >> this is "pbs newshour wkend," saturday. >> stewart: as we saw earlier in the program, there are major epncerns about g stoned drivers off the road. to bring you one more twist on this story from a researcher in massachusetts. turns out that just like everything el these days, if u want to find out whether you're too high to drive, well, there's an app for that. >> so, you're tracking the hand/eyeround-- so, coordination-- while you're also counting squares that flash on the screen. >> sreenivasan: gt.ot all right. l milburn has developed druid, an app that tests cognitive and coordination ability. i'm establishing a baseline on druid, testing myself when i'm supposedly sober. >> and your finger was on the circle about 25% of the time. >> politicians and police were saying, "we have no way to measure, you know, impairment from cannabis." and i've been a psychology professor for 40 yes now and one of my areas ofha speciay been methods, measurement and statistics. and i thou