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If you google EV numbers you will find many explanations as to how they are derived, just so that you understand better the "reason" for the number.
To answer your question the EV number for a 25 ASA should be 1.4
One EV number signifies a stop or doubling the light, or in this case the sensitivity of the film. For example, if as ASA 100 I have a reading of 13 at 200 ASA I would have a reading of 14 and at 400 ASA I would have a reading of 15. Going the other way I would have a for ASA 50 a reading of 12 and for ASA 25 a reading of 11.
For your example, as you can see all you have to do is substract 2 units and you should meter for a value of 1.4.
Good luck.
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