Like Mitchell, I have to disagree with you Elaine - see this thread
started by McAngus about 4476661V1 and 'her sisters'.
I believe that we've been asked to click on the furthest-observable terminal
particle in a potential track, i.e. the left-most black dot
of your graphic and, regarding 339373V1, the one arrowed here (I aplogize for the poor-quality images in this post):
I think we're all by now aware that there seem to be only two similar-looking CM sample tracks, as shown above, pasted this-way-that-and-the-other, but one (track #2) with the terminal particle (black) about twice as distant from the central blob (red) compared to the other (track #1).
Also, as tudorbug implies, and as was eventually confirmed in the above thread, the team have a generous 30 pixel radius of tolerance (60 pixels diameter).
So one will almost always
get away with clicking the central blob (Elaine's red
dot) in the case of small-to-medium-sized versions of either sample track, and mostly so in the case of larger versions of the shorter sample (#1), but not necessarily of the longer one
(#2). I'm pretty sure, as Mitchell says, that it is Elaine's black
dot that in either case they are in fact after (i.e. the terminal particle that they would be interested in analysing, rather than the central 'blob' that is most likely due to aerogel impaction - see below).
Regarding 339373V1 then, my rough measurements from the screen are that the central blob is at ~152/33, the further terminal particle at ~128/21, the radial distance between them in pixels being ~28, i.e. just (but only just) within the acceptable limit. But it would only take a pixel or two's difference in the team's logging of the location of these features for the 30 pixel limit to be exceeded.
Meanwhile, I've found (without exception so far) that if ever in total doubt about where to click, particularly when the track is very faint,
fuzzy or crossing the frame edge, a reasonable compromise is to click halfway between where you think those two regular features may be.
I'm sure (at least hope) that some sort of latitude regarding where one may click on a potential track within real
movies (which may well have a quite different characteristics to the two CM samples) will be sufficient to alert the team to something worth reviewing, which has to be the point of our participation after all.
In which regard it's worth reproducing what DanZ said in the above thread, i.e. that he ..." was told the 'big blob' is some messed up aerogel, but I've asked again. Regardless, whatever it is, it's not the terminal particle, but because it was there to begin with, it was included for every cut and paste used for the CMs ... but please understand, the scientists and technicians on this project are very busy analyzing particles and trying to get more tiles scanned. So as long as dusters now know where to click, they're not too concerned with blemishes or how much leeway are in the CMs ...".
Personally, I'm not sure whether that's reassuring or not.
: it would have been better if I'd reproduced DanZ's subsequent post
, that the central 'big' blob (at least in the case of the Orion-based CM) has unambiguously been confirmed to be composed of condensed aerogel, as is typical of all cometary particle tracks on the opposite side of the collector].