N. D.: Normal Distribution
https://www.researchgate.net/figure/Post-intravenous-immunog...
NCS-nerve conduction study,
NCV N.D- nerve conduction velocity normal distribution

https://en.wikipedia.org/wiki/Normal_distribution

In probability theory, a normal (or Gaussian or Gauss or Laplace–Gauss) distribution is a type of continuous probability distribution for a real-valued random variable.

https://ar.wikipedia.org/wiki/توزيع_احتمالي_طبيعي

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Note added at 28 mins (2021-05-25 12:42:54 GMT)
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يمكنك اختصار المصطلح على هذا الشكل
ت.ط
ثم توضيحه أسفل الصفحة

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Note added at 4 hrs (2021-05-25 16:55:08 GMT)
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To elaborate a little further, seeing how this abbreviation can stand for many different things, it's important to pay attention to the context. not determined/not done... is appropriate where a value (or lack thereof) is expected. But in our case the abbreviation is a column header, i.e. it refers to a property or attribute with values for each row.

Here is another example where the abbreviation does not refer to a property



https://watermark.silverchair.com/1250996.pdf