The Number of Taps tab in Design Options allows you to specify constraints on the number of taps (NTaps) your filter can have.  There are three categories of NTaps constraints:

1. Limits - sets the minimum and maximum number of taps
2. Even/Odd Constraints - optionally constrains the number of taps to be even or odd
3. Multiple - sets a value that the number of taps must be a multiple of

Limits

When your filter is first created, the minimum/maximum limits are set to the minimum/maximum limits that ScopeFIR allows for the filter's design type.  However, you can increase the minimum, or decrease the maximum, at any time, so long as you stay within the original limits.  This is useful, for example, for designing a FIR filter that will be implemented in hardware using a FIR filter chip that requires the number of taps to be within some range.

Even/Odd Constraints and Multiple

Some FIR applications require the number of taps to have special numeric properties.  For example, multi-rate FIR implementations often require that the number of taps be a multiple of the change in sampling frequency at that stage.  ScopeFIR allows you to constrain the number of taps to be None, Odd or Even, and also to be a Multiple of some number.

If you enable both Odd and Multiple of, the multiple itself must be an odd number.  Note, however, that if you set the even/odd constraint to None but specify an odd number for multiple, the number of taps may be even.  For example, if the constraint is None and the multiple is 5, the number of taps could be 10.

Estimates

Estimates for the number of taps also may be constrained.  If you check the Constrain Estimates box, estimates will be adjusted from the best estimate to closest value which meets all constraints.  Otherwise, when the Constrain Estimates box is un-checked, estimates of the number of taps will be unaffected by the constraints.  Constrain Estimates is checked by default.