The present invention relates to a method of distributing a skin care product to a subject, the method including the steps of: obtaining a sample of interstitial fluid from the skin of the subject; measuring the amount of a skin analyte in the sample; and distributing a skin care product to the subject to alter the amount of the skin analyte in the skin of the subject. The reflecting optical element is disposed at a first side of the carrier. In further embodiments, the particles are generally spherical or at least substantially spherical. By placing the switches closer to the device under test, the device operates on the tester in conditions more closely approximating electrical environment as it would in actual use. This information can be used to allow a user to keep phone numbers in hisher contact list in any common format on hisher country of origin and still allow numbers to be dialed correctly when the user is travelling anywhere in the world.