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PSO,  CtP,  L*/a*/b*,  Delta-E,  plusminus,  ISO  ...
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The secret of unambiguous colour definition
 Not to recognize immediately but nonetheless of most importance at the VierFarbSelector is its typical representation of optical colour solitaires. 
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At the VierFarbSelector colour tones are only built up with Black, if at least one of the 3 basic colours Cyan, Magenta and Yellow is saturated and has therefore the percentage of 100%. In the above example it is Cyan. 

That means: Changing the value of the black part of a colour tone will optically result in another colour tone
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At a GCR colour chart, where one black screen after another is laid over all colours per page in total, a multitude of optical colour duplicates will be created, which are only different by their numerical composition of C, M, Y and K.
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That means: Changing the value of the black part of a colour tone may optically result in another colour tone - or in the same.  

But how to control the impression of a colour at prepress or later, if the scanner operator has chosen another "GCR value" as the graphic artist?
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Additional: The mixture of chromatic and achromatic values for colour tones is leading to a serious deviation from the latest Media Standard, which is fixing the CMYK composition under 50% GCR. This "GCR value" can already be reached with 10% Black at Pastel colours, or with 60% Black at dark colour tones - but who knows the resulting colour BEFORE scanning?
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Highly precise colour definition
of the VierFarbSelector through representation of the CMYK colour tones on the official paper grades for offset printing according the latest Media Standard from bvdm (Confederation for Printing and Media in Germany), according the guidelines for the PSO- certification (Process Standard Offset) as well as the standard for newsprint according ISO 12647-3:2005 with 26% dot gain in the area of 40/50%, which is valid since July 2005 worldwide.

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The production
of the new VierFarbSelector colour charts, completed in April 2006, was done by using the Computer-to-Plate process (positive copy) with printing machines of the latest generation and with ultramodern measurement technique and control engineering. This technique resulted in an unusual exact constancy of the colour values over the sheet width and the edition.
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The spectrum metric tolerance
for the solid tones of CMYK according L*/a*/b* - colour coordinates could (e.g. at paper grade 1 and 2, which are used mostly), be kept under Delta-E = 2,35 (allowed Delta-E = 5). The dot gain tolerance for the halftones could be kept at plusminus 1% at 13% in the 40%-area (allowed plusminus 4%). Likewise the grey balance was checked carefully and permanently by using the media control bar for the optically same impression of the basic colours CMY versus Black.
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It has been printed:
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A)  Offset printing according ISO 12647-2:2004: 
Paper grade 1: Illustration paper woodfree, glossy coated, 70g/m2 plus     
Paper grade 2: Illustration paper woodfree, (silk)matt coated, 70g/m2 plus
Paper grade 3: LWC paper woodpulp, machine coated, approx. 65g/m2     
Paper grade 4: Offset paper woodfree, uncoated white2     
Paper grade 5: Offset paper woodfree, uncoated yellowish (ivory)2     		 .
VierFarbSelector:  250g/m2
VierFarbSelector:  250g/m2
VierFarbSelector:  070g/m2
VierFarbSelector:  250g/m2
VierFarbSelector:  250g/m2 

For instance, according to the latest Media Standard, the screen for paper grade 1 and 2 may be between 150 lines and 200 lines per inch, but - different from the past - the dot gains have to be the same for all those screens and to be adjusted by the Computer-to-Plate process (CtP)! For the VierFarbSelector 150 lines per inch were chosen, an additional printing version with 200 lines per inch was consequently left out; as well as further papers for web offset, as only LWC paper is standardized and the VierFarbSelector is only representing Standards. 

The so called printing ink 'Europescale' - colloquially also described as 'Euroscale' - has become obsolete or is dissolved within the Standard ISO 12647. Therefore the printing ink is only called 'ISO 2846-1' for Offset and 'ISO 2846-2 Coldset' for newsprint. But in daily business it will be talked about as Euroscale furthermore for some time.
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B)  Newspaper rotary printing according ISO 12647-3:2005
Newsprint 54g/m2 (10% mechanical pulp, 90% recycled pulp) with ISO 2846-2 Coldset, 100 lines per inch.
Notice: Colour charts on newsprint, e.g. with 60 L/cm or not with standardized ink ISO 2846-2 Coldset do not represent the latest Media Standard.
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