Spreads 1

Key Spreads 1 in
IRS refers to an optional constant rate s that must be added to the product of the appropriate gearing from Gearings 1 and the applicable fixing of the index defined in Index 1 in order to produce the final rate used in calculating the floating cash flow amount.
If no index is defined in
Index 1, i.e. if the leg is fixed, the rate here is interpreted as the leg's fixed rate.

If omitted, a flat value of 0 is assumed.
Several values may be also entered here in the form of a
If n values are provided, then the first n cash flows are paired with the provided n values in successive order.
If any cash flows are left over, they will use the last value.
Look at
IRS for the exact mathematical formula.