He ran the program. The screen flickered. Instead of the familiar gray interface of the 6.4 version, a black window appeared with white text: Enter Duct Parameters to Begin.

The file was suspiciously small—just 2.4 megabytes. No modern design tool was that lean. His antivirus flinched, then fell silent. An icon appeared on his desktop: a silver duct elbow with glowing blue eyes. He double-clicked.

If you are seeing a "Version 64" on a download site, it is highly likely one of three things:

While the full version is paid, Elite Software offers a free evaluation of Ductsize 6.0