For what ?
As the article here points out the value changes with paper type/printer/profile.
The smart thing to do is use the chart David's provided, or one you've built yourself, and test for your own specific set up. It only takes a single sheet of paper. As the article mentions different papers can have significantly different threshold values.
Another interesting thing you can discover from the test is how much viewing light effects perceived shadow detail. You can target specific prints for their intended lighting conditions.
I think the writer of that article should have mentioned calibration/linearisation first in that article. With a printer/ink/media preset/paper that does not have that condition you could be wasting potential dynamic range and time when you adapt the methods described. Where analogue print making had a somewhat linear range (neg+pos) or at least a continuous one between the thresholds it does not have to be like that with inkjet printing.
The viewing/display light conditions was what I missed in that article too. I checked for framing behind glass and viewing light, both can cause the shadows to block even when the paper's dynamic range is wide enough. In a sense a paper linearised for the printer and its inks already meets the threshold conditions he describes, the (B&W) printer profile made of that condition should be enough. Enough viewing light should match that. It is in the display condition and display light conditions that shadows still can block. If viewing light is adapted to the expected display conditions one can correct the shadows and more with curves based on a proof print or a print of the targets discussed and add a curve like that to the print filters of Qimage for example. Image content should not be forgotten in that phase. I do not think a curve based on the targets + the adapted soft proof replaces a real proof print, it helps though.
Several 21 step wedge images have short expanded shadow + highlight ranges next to the main one. Can not recall where I got the "Technical" one from but it has the 21 step next to a continuous one and shadow + highlight ranges + 4 well chosen images. B&W all. A print made with it after linearisation/profiling tells a lot in different viewing conditions.
There is also a bit of confusion created by the writer. 90% of photographers have a workflow that uses RGB-device printer profiles. There is an RGB>CMYK translation in all the workflows but it does not happen in the RGB-device printer profile for most. Media presets have that translation or part of it baked in. With a RIP the printer profile usually holds way more of the RGB>CMYK translation so for that condition he is right
Met vriendelijke groet, Ernsthttp://www.pigment-print.com/spectralplots/spectrumviz_1.htm
July 2013, 500+ inkjet media white spectral plots.