This experiment provides correlations between a carbon and its attached protons.  The constant time (CT) version of H—C HSQC is normally used as it circumvents the issue of splitting of signal due to homonuclear C—C J couplings which reduces spectral resolution.  The "constant time" refers to the entire evolution period between the two INEPT steps which is kept constant in this experiment.  If this evolution period is set to be the inverse of the J-coupling constant, then the sign of the magnetization of those carbons with an odd number of aliphatic carbon attached will be opposite to those with an even number.  For example, if the C of leucine appears as a positive peak (2 aliphatic carbons attached), then the C (3 aliphatic carbons attached) and C (1 aliphatic carbons attached) would appear negative.