From: usenet@listmail.good-stuff.co.uk 
  
 On 11 Aug 2025 10:01:46 GMT, Roger Hayter  wrote: 
  
 > 
 >Thinking more, should it be expressed as "82m  AOD"?  That would make sense. 
  
 That's what it means in practice, yes, and that's how you would write it 
 outside a purely technical context. 
  
 The reason that the 'm' is attached to the 'AOD' in a technical context is 
 that there are a number of different ways of measuring water levels, so for 
 clarity it's always expressed as a single string comprising the unit of 
 measurement and the relative datum. You can, for example, get data expressed 
 in mmAOD, or mASD, or mBDAT, to name but three. It also makes it clear that 
 the unit and the datum are inseparable - a value of, say, 82m is meaningless 
 without the datum, so including the datum with the unit as a single text 
 string ensures that you'll never get an un-datumed value. 
  
 Mark 
  
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