1. Timers are designed to permit a wide variation in the DC supp[y voltage without affecting the output frequency or single-pulse duration. Another reason is that the equations determining the frequency or timing were little more that approximate, despite the appearance of great precision in the textbooks- modern
  2. Timers will work very closely to the way the textbooks - modern
  3. Timers will work very closely to the way to textbooks say they do. Electronic circuit guidebook, volume 2
  4. Timers will show you how it is done.
  5. Part 1- overview of IC Timers 
  6. Part 2- timer projects and circuits.