Although there are rather simple rules determining the pronunciation of "the", native speakers quite often deviate from these rules (including, e.g., TV shows). According to the Longman Pronunciation Dictionary,


  The EFL learner is advised to use [ðə] before a consonant sound (the
  boy, the house), [ði] before a vowel sound (the egg, the hour). Native
  speakers, however, sometimes ignore this distribution, in particular
  by using [ðə] before a vowel (which is in turn usually reinforced by a
  preceding ʔ), or by using [ði:] in any
  environment, though especially before a hesitation pause. Furthermore,
  some speakers use stressed [ðə] as a strong form, rather than the
  usual [ði:].


My question is: when native speakers use [ðə] instead of [ði] before a vowel sound, do they do it on purpose or accidentally? If it is on purpose, how do they (typically) decide which pronunciation to use? What is a valid reason to use [ðə] before a vowel sound?


Question: Which products should have FCC certification and about how much does that cost?
Answer: Where I used to work we saved a lot of money on CE testing by hiring the facility for half a day and doing our own preliminary testing. We fixed any problems, they were usually quite minor, and the equipment always then passed first time. You do need to have someone who knows how to drive the test instruments, of course.