Controlling the state of bicycle components I tried to formalize the maintenance of a bicycle. Every component must be periodically checked using the following algorithm:

Begin
    1: Wait for appropriate time
    Measure the component wearout
    Is it ok?
        yes: go to (1)
        no:
            Is the damage critical?
                yes: replace
                no: repair
End


Every component has a method of measuring it's state. The best one is a special tool, giving the precise value of wearout. But not every one has it. I created a table for all the components I could think of:

|------------------------------+---------------------------------------------|
| Component                    | Measuring method                            |
|------------------------------+---------------------------------------------|
| Chain dirty, needs           | Visual inspection.                          |
| cleaning and lubrication     | Chain links become stuck to each other.     |
|------------------------------+---------------------------------------------|
| Chain elongation             | Special tool                                |
| Rear cassette gears worn out | Special tool                                |
| Front chain ring worn out    | ?                                           |
| Tires                        | Visual inspection.                          |
| Tubes                        | ?                                           |
| V-brake pads                 | Feeling of bad breaking. Visual inspection. |
| Disk brakes disks            | ?                                           |
| Cables                       | ?                                           |
| Fork                         | ?                                           |
| Oil inside fork              | ?                                           |
|------------------------------+---------------------------------------------|


There are more component that also require inspection and replacement.

Can somebody fill in the question marks in my table?
For most of your ?s, I would use visual inspection.

If you always check your chain for wear, the chain rings and cassette will last a long time.

Some brake pads, rotors and rims have waer indicator guides built into them.

Fork is greased, not oiled. Fork is inspected for cracking, a weak point is below the crown.

Frame should also be inspected for cracks.