The Rate of Change (ROC) is similar to the Momentum.
The standard Rate of Change is the ROC 12 days : GT::Indicators::MOM->new()
If you need a non standard Momentum use for example : GT::Indicators::MOM->new([9]) or GT::Indicators::MOM->new([25])
This Indicator was validated by the data available from comdirect.de: The DAX at 04.06.2003 (data from yahoo.com) had a ROC of 8.05. This is consistent with this indicator: 8.0451