Spurious clock modulation and jitter create artifacts and noise in acquired signals and in reconstructed waveforms. Clean clocks are also important in ...
www.thinksrs.com/products/CG635.htm - 48k

http://www.atis.org/tg2k/_bit-by-bit_asynchronous_operation....

After going into the above website, please check out the terms "gating" or “slewing" the clock modulation. You can click onto "slewing" which is high-lighted in blue.

The above website appears as below:

bit-by-bit asynchronous operation: In data transmission, an operation in which manual, semiautomatic, or automatic shifts in the data modulation rate are accomplished by gating or slewing the clock modulation rate. Note: For example, bit-by-bit asynchronous operation may be at 50 b/s one moment and at 1200 b/s the next moment.


In Wordweb, the verb “to slew” means to turn sharply, change direction abruptly.


http://www.patentstorm.us/patents/7061331.html

Also, the above website refers to slewing (with regards to "clock")several times.

Clock generation circuits providing slewing of clock frequency ...
Clock generation circuits providing slewing of clock frequency - US Patent 7061331 from Patent Storm. Techniques are described for slewing a clock frequency ...
www.patentstorm.us/patents/7061331.html - 14k - Cached - Similar

This is just my interpretation because of the words in your description: 乗せ変え





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Note added at 2 hrs (2007-04-09 10:02:05 GMT)
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Excuse me sumc, my complete answer is "slewing the clock modulation rate" (from my example above) not just "slewing the clock."