FWIW oil Wt is a made up "standard" and has little or few controls or standardised tests, So AEs Wt is different to Losis and so on.
cSt is Centistokes, and has an official international standard and test procedure.
There shouldn't be any variation beyond tolerancing between two bottles of 250 cSt oil at room temperature.
(All sorts of things happen when you move away from room temperature and/or start using the oil as the compostion of the oil and additives used will affect how viscosity changes due to temperature/time/contamination/etc)
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