Such revision don't happen "out of the blue". Either there have been some inconsistencies or contradictions in context of ISO/IEC 17025:2018 (Section 7.8 ) or there have been inconsistencies in reportings of measurement results or applications of CMCs.
I think it may be because it doesn't state what that ppm is referring to. For example, we may have a 10 mV to 100 mV range with an uncertainty of 23ppm + 12μV the ppm can be seen as unclear if it relates to mV or μV. Plus ppm is an English acronym and possibly they would like to reduce them.
Lab 45 (6.10) has this to say about the use of %
Particular care should be taken when the unit itself is normally expressed in percentage terms;
examples are relative humidity (%rh) and amplitude modulation (% AM). For example,
50 %rh ± 10 %rh means the boundaries are 40 %rh and 60 %rh, whereas
50 %rh ± 10 % means the boundaries are 45 %rh and 55 %rh.
Under circumstances of this nature the presentation of the CMCs must be such that there is no
ambiguity in interpretation.
The last bit being the interesting one. Its interesting that electrical is used as the example so it clearly is some sort of comment on them. Though as a mech lab that is going for some 17025 stuff I think the below quote may give a reason for the mud slinging that might be going on. ;-)
Lab 45 6.17
In dimensional calibration, the schedules of accreditation for the calibration of basic dimensional
measuring tools and equipment have historically reported a CMC for parameters most relevant
to end users. This method however does not provide transparency with regards to auxiliary
measurements such as flatness and parallelism of micrometer measuring faces etc. These
additional measurement techniques shall be listed on the schedule of accreditation along with
the corresponding measurement uncertainty.
For years labs only needed to say the error of length and not mention the capability for flatness or squareness. It is a bit like having a multimeter calibrated and the only Uncertainty quoted is for the Voltage.
PPMs must live on. Not until inch and other nonsense units go away
Its interesting as officially you splitters have been using the metric system for a while, but for some reason subconsciously you still want to be back under British Rule
As I posted before in another thread, I was once confused during an installation in UK where the local engineer asked me about a wire size, using "mils", which I knew was not 0.001 inch. Unfortunately, he did not mean "mm", he meant "mm2".
Yeah, we use mil as an abbrev for mm. So "shave a few mils off that" and "I have some 2 mil wire" are common. I do get confuddled when you get places selling wire in Amperage, "yeah that is 12 amp wire". AWG, mm
2 and CSA at times do give me fun afternoons exp when a customer makes up some crimp samples for me but assumes I know the size of wire just by looking at it.
IMO, the demise of ppm is old news. I also lament the loss of micron, though it's still in so much common use that I don't think anybody's going to change anytime soon. In the US, a micrometer is a thing you use in the shop to measure with. I think angstrom is fading away but is still acceptable in the "outside SI" list at NISt.
So if PPM and PPB are old news then why are we getting people hear singing and dancing about how their meter is good to 1ppm.