My dearest S. gave me this and I'm in love with it. It's a tiny notebook that has 15 "idea" forms.
Each time you have an idea, you fill one up. It asks how much sleep you've had, if you've had any cultural input, what you've eaten or how original do you think this idea is.
When you've got 15 ideas, you can proceed to extract the information of the forms into graphs (at the end othe notebook) and then compare the data to find out when and how your creativity appears.
If you wish, you can send your reports to the creators so that a general study can be made.
See more here.