ICH GCP type of the data [GxP / QC / QA]
❝ “6.4.9 The identification of any data to be recorded directly on the CRFs (i.e. no prior written or electronic record of data), and to be considered to be source data.”
The matter is not totally well defined. And that's to your own advantage. Anything that you can record on CRF can be recorded there as source if it is meaningful to do so.
If paper: The alternative is to record on other source and then transcribe to CRF which sometimes is a source of plenty error (and thus often done in duplicate).
If electronic: Now the concept of a CRF is kind of imaginary. The CRF is basically just a print or a dump of info taken from all sorts of sources (like a database here, a textfile there, a recording sitting on a drive in Guadalajara, a fitbit record copied (true source would be on the wrist of the user) to a drive in Vladivostok but worn in Bilbao, and so forth).
If you look at it from an auditor's or inspector's perspective, it is convenient to know in advance what/where the source is, i.e. if the temperature of all subjects is recorded on CRF directly or written onto a piece of paper sitting with the TMF or trial binder somwehere.
Lots of freedom here
Pass or fail!