High-definition television:

Colour broadcasts started at similarly higher resolutions, first with the US NTSC color system in 1953, which was compatible with the earlier monochrome systems and therefore had the same 525 lines of resolution. European standards did not follow until the 1960s, when the PAL and SECAM color systems were added to the monochrome 625 line broadcasts.

Please answer a question about this article. If the question is unanswerable, say "unanswerable". How many lines of resolution did the US NTSC color system have in 1953?
525