Assertion: tone | /r/CapableOf | replace older busy tone
Facets:
Source sentences:
text: This tone was adopted in the mid to late 1960s and replaced the older busy tone, which was the same 400 Hz signal but at half the interruption rate (i.e. 0.75 s on, 0.75 s off).
text: This tone was adopted in the mid to late 1960s and replaced the older busy tone, which was the same 400 Hz signal but at half the interruption rate (i.e. 0.75 s on, 0.75 s off).