French term (edited): Verficiation du niveau de dropouts sur la même mire de 3 mintues........

I certainly wouldn't disagree with Charlotte's answer and excellent explanation, but would like to add a few obesrvations of my own.

The correct term is 'dropout' [one word, no hyphen]
Although as Charlotte says, the 'mire' may be referring to a 3-minute section of the tape (this happens to be just about the length of time for which one should run a cleaning cassette for test purposes), it MIGHT also mean a test chart, inasmuch as dropouts are easier to detect on static picture content. See if the 3-minute length of tape is mentioned elsewhere?

My take would be:
"Checking dropout level over same 3-minute test segment"

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Note added at 3 hrs 23 mins (2004-11-16 08:59:57 GMT)
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Just to say that I would tend to avoid Charlotte\'s linguistically superior \'ascertain\', since it feels out of place to me in my techie homeland. It is difficult to make an objective measurement of dropout level (needs specialist equipment), and to me \'ascertain\' suggests the idea of \'pinning down accurately\'. In practice, one probably simply looks at the picture and visually notes (roughly) how many dropouts pass --- or the same thing could be done using a waveform display device, or monitoring the d/o compensator control line in the video machine, for example.

So to me, using \'check\' or \'assess\' for \'vérification\' would imply something rather less exhaustive (cf. their own use of \'mesure\' vs. \'vérification\')