1. Oboe: The oboe is the highest-pitched instrument in the orchestra, and it sets the pitch for the rest of the instruments.
2. Clarinet: The clarinet is the next-highest pitched woodwind instrument, and it tunes to the oboe.
3. Bassoon: The bassoon is the lowest-pitched woodwind instrument, and it tunes to the clarinet.
4. Flutes: The flutes tune to the oboe.
5. Trumpets: The trumpets tune to the oboe.
6. Trombones: The trombones tune to the trumpets.
7. French horns: The French horns tune to the trombones.
8. Tubas: The tubas tune to the French horns.
9. Violins: The violins tune to the oboe.
10. Violas: The violas tune to the violins.
11. Cellos: The cellos tune to the violas.
12. Double basses: The double basses tune to the cellos.
This order is based on the fact that the higher-pitched instruments are more sensitive to changes in pitch, so they need to be tuned first. The lower-pitched instruments are less sensitive to pitch changes, so they can be tuned last.
The orchestra tunes using a tuning fork, which is a metal fork that vibrates at a specific pitch. The oboist plays the pitch from the tuning fork, and then the other instruments tune to that pitch.