With the DT-920 you get:

-Handunit DT-92
-Hand probe
-Density step

Operation of the DT-92:
The DT-92 is a measuring device for the photometric determination of the density of X-ray films.
The unit of density is defined by the logarithm of the ratio of light intensity before the film (lo)
to allow light intensity(ld)

S = lg (lo) / (ld)

From this it follows that, for example a film that only allows 10% of the amount of light the darkness occurring 1 and a film that can be 1% by the 2 density a film of only a thousandth of the amount of light has to pass through, hence the darkness 3, etc.
The transmitted light intensity is derived with a strictly linear over many decades, silicon photodiode.
In measuring the signal via a high-precision reference evaluated is converted into a digital value and an LCD to the police.
The measurement error is up to S = 5.0 within + / – 0.05.
This is for an ambient temperature of 10 ° to 35 ° C and a range of luminance of 15,000 – 80.000cd / m ⊃ 2; on the screen of the movie viewing device.
It can either be in absolute as well as worked in relative mode.