Hi. Basically, how are hairsprings measured?.
I need to change the one in the picture as it is distorted and beating too fast.
I understand about mainspring measurement but how about hairsprings?.

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The post is in the pocket watch section, perhaps it would do better in clocks.

Hairsprings are vibrated to fit each different watch / clock escapement. Does this one have a over coil. Unless you are an experienced watchmaker. It would be nearly impossible to replace your self.

The one on your clock escapement most likely can be straightened.

If it is not mangled ie. "kinked" then certainly untangling it is preferred to replacing it. I have found good luck using #5 and #7 curved tweezers close the door to the shop and take your time. What ever you choose to do with it "good luck"
Regards, John

Stephen, Two things;

First your movement looks like a "Carraige" type that was assembled to a larger non-carraige" type clock dial.

Second, a replacement hairspring for that movement qualifies as an "un-obtanium" grade part . . . meaning as it is still running, straightening the damaged spring is a far better and most practical "fix".

Our own hairspring master, Chris Abell could probably be persuaded to take on that task.

You can also check Timesavers who sell a varietyof complete replacement platform escapements like yours.
http://www.clock-parts.com/cat...Level=2&ProdID=23105

Thanks everyone for taking the time and trouble to reply.