Round Ports Per WinISD

Click on the figure (ex. 3.23 in.) until it is highlighted.  Then type in the inside diameter you wish to use.  When you save your project your diameter will be saved, too.

You will also note that placing the cursor arrow on the measurement type (in., l., mm, etc.) and clicking goes through the progression of measurement types.  The program calculates the equivalents.

The program is not so US user-friendly that it knows the diameter of PVC at Home Depot.  It was developed in Sweden.  I believe you see the equivalent of a metric unit when you look at the oddball sizes in inches that come up as default.  If your default setting was mm, the numbers that come up would make more sense.

Note:  You should read everything in the Help section.  This information is contained in the "Using WinISD Pro" section.

I would choose round and buy a premade port tube, cut length to specs.  In some situations round is not possible because of available front baffle space, so slot is used, although the construction of a bulkier slotted port will necessarily add to the enclosure volume.  You probably would not be able to hear any difference, though, if either port were built to specs, so choice might be a matter of available space and aesthetics.

This enclosure is aesthetically pleasing, and the slotted port configuration was used because there was no room for round ports on the face.