I think that CWT stands for Counter Weight. WT is a standard abreviation for weight, and Counter Weights are used on stages (see the reference below).

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Note added at 2001-12-27 09:53:19 (GMT)
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Sorry I forgot to translate ¥"floor.¥"
Looking at the diagrams of counter weight systems at
http://www.gweep.net/‾prefect/pubs/iqp/node54.html
and at
http://www.wpi.edu/Academics/Depts/HUA/TT/TTHandbook/rigging...
And bearing in mind that each of the two ¥"floors¥" corresponds to a certain elevation, I would say that these floors correspond to lowest levels of the counter weights - hence 最低位（置）
or it might be an alternative word for the
¥"loading bridge¥" or ¥"weight rail¥". Yes. I would go for the second suggestion since it is seen to correspond to another ¥"rail¥" (the automation rail). You need to see a diagram but I suggest ¥" counter weight loading platform¥"
カウンターウェイト・ローディング・プラットフォーム

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Note added at 2001-12-27 09:54:19 (GMT)
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Actually, why not stick with ¥"bridge¥" hence -
カウンターウェイト・ローディング・ブリッジ

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Note added at 2001-12-27 10:10:01 (GMT)
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There are words such as
フライ・ギャラリー fly gallery
フライ・ブリッジ fly bridge
and just
ブリッジ
to refer to similar constructions. So perhaps
カウンターウェイト・ブリッジ
would be better. In any event the following glossary should be useful.
http://www.inabun.or.jp/users/butai/kikou/gekijyou.htm