usb(3): avoid non-printing math symbols
 [rsc] --rw-rw-r-- M 1328934 glenda sys 6941 Mar 28 12:38 sys/man/3/usb
	/n/sourcesdump/2006/0328/plan9/sys/man/3/usb:134,143 - 
	/n/sourcesdump/2006/0329/plan9/sys/man/3/usb:134,144
	  .PP
	  The data rate is thus
	  .IR hz × samplesize
	- bytes per second, and the packet size used will vary between
	- ⌊(\f2period\fP×\f2hz\fP)/1000⌋×\f2samplesize\fP
	- and
	- ⌈(\f2period\fP×\f2hz\fP)/1000⌉×\f2samplesize\fP.
	+ bytes per second, and the number of samples in a packet
	+ will be 
	+ .RI ( period × hz )/1000,
	+ rounded up or down.
	+ Packets do not contain fractional samples.
	  .PP
	  The mouse, which produces 3-byte samples, is configured with
	  .BR "ep 1 bulk r 3 32" :