"fold sphere" meaning in English

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  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
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          "ref": "2006 July, Burge et al., “Design and analysis for interferometric measurements of the GMT primary mirror segments”, in Proceedings of SPIE, volume 6273, →DOI, retrieved 2021-12-27, pages 62730M-5",
          "text": "Center of curvature for the 3.75-m fold sphere is accessible for in situ testing of this mirror.",
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      "glosses": [
        "A fold mirror that is a \"sphere\", i.e. a spherical mirror"
      ],
      "id": "en-fold_sphere-en-noun-hZL1VnOj",
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        [
          "fold mirror",
          "fold mirror"
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          "spherical mirror",
          "spherical mirror"
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      "related": [
        {
          "word": "fold flat"
        }
      ]
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  "word": "fold sphere"
}

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  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "related": [
    {
      "word": "fold flat"
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          "ref": "2006 July, Burge et al., “Design and analysis for interferometric measurements of the GMT primary mirror segments”, in Proceedings of SPIE, volume 6273, →DOI, retrieved 2021-12-27, pages 62730M-5",
          "text": "Center of curvature for the 3.75-m fold sphere is accessible for in situ testing of this mirror.",
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        }
      ],
      "glosses": [
        "A fold mirror that is a \"sphere\", i.e. a spherical mirror"
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  "word": "fold sphere"
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