i couldn't find anything else on bringing a non electronic health/fitness device (calf stretcher) like this and using it between games during a USTA match etc
http://www.amazon.com/s/?ie=UTF8&ke...vptwo=&hvqmt=b&hvdev=c&ref=pd_sl_5js7575m26_b
USTA Comment 30.1: A player may bring to the court written notes that were prepared before the start of the match and may read these notes during the match. A player may not use electronic devices such as cell phones, digital messaging systems, radios, mp3 players, cd and dvd players, cassette players, and any device capable of receiving communication. Hearing aids and watches not capable of receiving messages are permitted. A player desiring to use any other electronic device should first ask the Referee whether the device may be used.
http://www.amazon.com/s/?ie=UTF8&ke...vptwo=&hvqmt=b&hvdev=c&ref=pd_sl_5js7575m26_b
USTA Comment 30.1: A player may bring to the court written notes that were prepared before the start of the match and may read these notes during the match. A player may not use electronic devices such as cell phones, digital messaging systems, radios, mp3 players, cd and dvd players, cassette players, and any device capable of receiving communication. Hearing aids and watches not capable of receiving messages are permitted. A player desiring to use any other electronic device should first ask the Referee whether the device may be used.