The calculator itself looks good. The output drill values in "Number of 64ths" (e.g.) are a little odd, but I understand what they mean. I feel like the rest of the verbiage and some other bits could use tightening up though.
Here is an article in Peak of Flight on streamer sizing by Tim Van Milligan.
Agreed, it should allow one port as an option.
With all of the materials, manufacturine techniques, packing/ storage and aspect ratios used in streamers you will not be able to come up with a perfect calculator. There are some interesting research papers on flags and streamers that focuses more on the material mass and frequency of oscilation in a given airspeed that determines the drag. The problem with a calculator is that you would need to know the frequencies of each material and width and length, which requires a lot of testing. This is why most hobby calculators are simple and focus on mylar, nylon, and plastic streamers in a 10:1 or 12:1 aspect ratio and are meant for low or mid power. The ultra high aspect ratio, tracking streamers that have been flown lately are very inefficient, due to burbles and unique airflow the drag is next to impossible to accurately calculate.
The ideal would be, IMHO, to enter the original length and diameter, then choose from a drop-down box whether to enter the new diameter, length, or scale. You might also offer space for other dimensions that will be scaled by the same factor; these can be diameters, lengths, or any other dimension that the user wants scaled. For extra credit, use user entered labels for these additional scaled dimensions.
