From JP Morgan's Trading Credit Curves 1 we have that:

The MTM of a CDS contract is (for a sell of protection) therefore:

$$\text{MTM} = (S_{\text{Initial}}-S_{\text{Current}}).\text{Risky Annuity}_{Current}.Notional$$

Why do we need the Risky Annuity Current? I dont see the logic behind this...