Table 1. Definitions of variables and their identifiabilities in rKFP.
| Symbol | Meaning | Identifiable in rKFP |
 (uppercase) |
metabolite  or it pool size (absolute quantitation)
|
No |
 (lowercase) |
signal of the pool size (relative quantitation) | Yes |
|
concentration of  C-labeled  (absolute quantitation) |
No |
|
signal of  C-labeled  (relative quantitation) |
Yes |
|
the fraction of  in  , 
|
Yes |
|
the fraction of  in  , 
|
Yes |
|
flux | No |
|
rate, 
|
Yes |
|
proportionality constant between signal (relative quantitation) and concentration (absolute quantitation) of  , 
|
No |
 (subscript  ) |
a quantity of control | – |
 (subscript  ) |
a quantity of condition | – |
|
relative change of pool size, 
|
Yes |
|
relative change of flux, 
|
Yes |
|
ratio of pool size, 
|
Yes |
1: Which one of the two possible meanings is meant should be inferable from the context when not specified; it is a slight abuse of notation customary in the field (e.g., [46]).