Next time you are in the Post Office picking up "components", perhaps a roll of stamps is in order.
http://health.nytimes.com/health/guides/test/erection-self-test/overview.html?scp=1&sq=Nocturnal%20Penile%20Tumescence%20(NPT)%20test&st=cse
http://health.nytimes.com/health/guides/test/erection-self-test/overview.html?scp=1&sq=Nocturnal%20Penile%20Tumescence%20(NPT)%20test&st=cse