Does not appear that Hitachi makes exact display dimensions available on their site. However, using a bit of trigonometry and a simple ratio, it is rather straightforward step to arrive at the answer you desire. You might refer back to this
post regarding 17" displays, as the method employed is identical.
We know the screen itself has a diagonal measurement of 15", with an aspect ratio of 4:3. Through the use of a simple proportion and the work of Pythagoras, you should find that :
NP5690 (or similar) 15" UXGA 4:3 screen : 12.0 (w) x 9.0 (h) inches
Converting to millimeters (1 inch = 25.40 mm):
NP5690 (or similar) 15" UXGA 4:3 screen : 304.8 (w) x 228.6 (h) mm
For those who may doubt the accuracy of the above, you might consult this
link to a 15" UXGA display on the LG-Philips website. Comparison between the calculated dimensions above, and the listed specifications on the site are quite similar. Nearly all 15" 4:3 aspect ratio displays will be identical in measurement (in fact, you might peruse the different LG-Philips models of various resolutions
on the aforementioned site, and find the dimensions are all quite the same. All 15" models begin "LP15", btw).
Of course, you could always find a ruler or some other appropriate measuring device, measure the screen yourself, and simply convert from inches to milimeters. The conversion from inches to millimeters can be found above.
Nu Shield films are excellent, btw. Have been using them in my PDA for quite a while. The entire idea behind how Nu Shield films function is that the film does not adhere to the surface itself, but rather floats above it, secured by the screen bezels. As such, the film dimensions do not need to be completely accurate, as a portion of the film slides under the screen bezel itself. Ergo, the dimensions of your particular screen need not be precise to the micrometer for the purpose of purchasing a Nu Shield.
Do hope this helps.