[
 {
  "value": "1420405751.768",
  "sigma": "0.002",
  "source": "Hellwig, Vessot, Levine et al., IEEE Trans Instrum Meas 19, 200 (hydrogen maser vs caesium)",
  "year": "1970",
  "field": "radio spectroscopy",
  "id": "S1",
  "unit": "Hz",
  "quantity": "hydrogen ground-state hyperfine interval",
  "grade": "primary abstract, PRIOR-ART row 15",
  "bound_low": "",
  "bound_high": "",
  "recalled": "no"
 },
 {
  "value": "4463302000",
  "sigma": "4000",
  "source": "MuSEUM collaboration (J-PARC), muonium ground-state hyperfine 4.463302(4) GHz",
  "year": "2021",
  "field": "radio spectroscopy",
  "id": "S2",
  "unit": "Hz",
  "quantity": "muonium ground-state hyperfine interval",
  "grade": "secondary (search listing), PRIOR-ART row 14",
  "bound_low": "",
  "bound_high": "",
  "recalled": "no"
 },
 {
  "value": "203389100000",
  "sigma": "740000",
  "source": "Ritter, Egan, Hughes and Woodle, Phys Rev A 30, 1331 (and thesis 1984)",
  "year": "1984",
  "field": "radio spectroscopy",
  "id": "S3",
  "unit": "Hz",
  "quantity": "positronium ground-state hyperfine interval",
  "grade": "primary abstract, PRIOR-ART row 14",
  "bound_low": "",
  "bound_high": "",
  "recalled": "no"
 },
 {
  "value": "115271201800",
  "sigma": "500",
  "source": "Mueller et al. 2001, CDMS catalogue, as tabulated in A&A tables",
  "year": "2001",
  "field": "molecular spectroscopy",
  "id": "S4a",
  "unit": "Hz",
  "quantity": "CO J 1-0 line",
  "grade": "secondary tables, PRIOR-ART row 16",
  "bound_low": "",
  "bound_high": "",
  "recalled": "no"
 },
 {
  "value": "230538000000",
  "sigma": "500",
  "source": "Mueller et al. 2001, CDMS catalogue, as tabulated in A&A tables",
  "year": "2001",
  "field": "molecular spectroscopy",
  "id": "S4b",
  "unit": "Hz",
  "quantity": "CO J 2-1 line",
  "grade": "secondary tables, PRIOR-ART row 16",
  "bound_low": "",
  "bound_high": "",
  "recalled": "no"
 }
]