Incorrect message

[acwatic]

Tried installing TTW onto an SSD with a small capacity (240 GB). The installer reported an error that at least 17 GB free space is necessary for installation; however, this error was reported with as much as 19.8 GB of free disk space.

[The Many]

Software can have different methods of checking and reporting free disk space. It's normal for discrepancies like this to exist. For example, all of my "2TB hard drives" are reported as 1.81 TB in Windows. My 500 GB are reported as 465GB, and so forth. This is because of a key difference in how they're counting. Hard drive manufacturers use decimal (base 10), while Windows counts in binary (base 2). So for the former, 1,000 bytes = 1 kilobyte, but for the latter, 1,024 bytes = 1 kilobyte.

The wording of the message may be confusing to you, but it's not incorrect. Computers don't make mistakes and the bottom line is that you don't have enough disk space to install the mod. Free up a couple of GBs.

[acwatic]

Hard drive manufacturers use decimal (base 10), while Windows counts in binary (base 2). So for the former, 1,000 bytes = 1 kilobyte, but for the latter, 1,024 bytes = 1 kilobyte.

I know, but 1. it was Explorer telling me that I had 19+ GB on my drive, and as far as I can tell, it uses binary units, and 2. the discrepancy isn't enough to fail an installation. (18 GiB < 19.4 GB, the upper limit of "17 GB" and the number reported by Explorer)
I've installed it, but the fact remains the message is incorrect (or Windows reports more disk space than exists, which I sincerely doubt).