  Using a near-IR stellar library of 706 stars with a wide coverage of
atmospheric parameters, we study the behaviour of the Ca II triplet strength in
terms of effective temperature, surface gravity and metallicity. Empirical
fitting functions for recently defined line-strength indices, namely CaT*, CaT
and PaT, are provided. These functions can be easily implemented into stellar
populations models to provide accurate predictions for integrated Ca II
strengths. We also present a thorough study of the various error sources and
their relation to the residuals of the derived fitting functions. Finally, the
derived functional forms and the behaviour of the predicted Ca II are compared
with those of previous works in the field.
