Chain tightening vs replacement

[roadahead]

Hi all. I have a chain that clearly needs tightening but my question is when do you know whether it's time to replace it altogether? I'm not the original owner of my 1978 CB750F, so there's no way of knowing whether this is the original chain however I assume that it is.

I'm up for the challenge of tightening the chain but replacing it altogether has me a little bit puzzled/nervous. It seems like there are some specialized tools involved in the process. So what are the symptoms involved or things to look for that would indicate that it's time to replace the chain and sprockets?

 

[crazypj]

gently lift the lower run of chain with one hand to remove all slack then try and lift it off sprocket at 3 o'clock position with other hand
If chain moves more than about 1/16" it's time for chain and sprocket set

 

[Walms]

I look at the sprockets to see if there is any noticeable wear on the teeth and to check the chain for stretch, pull on the chain half way through where it is engaged with the rear sprocket. I believe rule of thumb here is anything more than a half the roller diameter is considered stretched too much.

Stretched chain

Worn sprocket