Pete------"...the former are measurable in the present,but dating relates to the past,and as i understand it involves assumptions which are not verifiable."

They ARE verifiable. read the details (yes, I know it's beyond either of us to understand ALL the math and chemistry, but basic facts can be found. You may read as much as your brain will tolerate...but don't get hung up on all the math...just note that they are constantly refining both measurement techniques and analysis parameters! They have no interest in making their data fit pre-established goals. They want correct answers.

Here is the basic quote:(I have highlighted the main point) ". When an organism dies, it contains a ratio of 14C to 12C, but, as the 14C decays with no possibility of replenishment, the ratio decreases at a regular rate. This rate is known as the half-life of 14C. The measurement of 14C decay provides an indication of the age of any carbon-based material (a raw radiocarbon age).[4] However, over time there are small fluctuations in the ratio of 14C to 12C in the atmosphere, fluctuations that have been noted in natural records of the past, such as sequences of tree rings and cave deposits. **These records allow for the fine-tuning, or calibration, of the indications derived from measuring the carbon ratio.** A raw radiocarbon age, once calibrated, yields a calendar date."
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Next relevant quote:"The above calculations make several assumptions: for example, that the level of 14C in the biosphere has remained constant over time.[15] In fact the amount of 14C in the biosphere has varied significantly, and as a result the values provided by the equation above have to be corrected by using data from other sources, using a calibration curve, which is described in more detail below."
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It goes on to explain the various ways that calibration is cross-checked to avoid serious errors. The experts do know that 14C variation must be accounted for... and they take special pains to deal with it!
The point is- No one claims this is accurate to exact days & weeks, but given known laws of physics and chemistry, combined with VERY accurate calibration against absolute known ages...such as in tree rings... it IS possible to reduce the possible errors to a very small range.


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Later in the article:"The 2004 version of the calibration curve extends back quite accurately to 26,000 years BP. Any errors in the calibration curve do not contribute more than ±16 years to the measurement error during the historic and late prehistoric periods (0–6,000 yrs BP) and no more than ±163 years over the entire 26,000 years of the curve, although its shape can reduce the accuracy as mentioned above.[47]

In late 2009, the journal Radiocarbon announced agreement on the INTCAL09 standard, which extends a more accurate calibration curve to 50,000 years.[48][49] The results of research on varves in Lake Suigetsu, Japan, which was announced in 2012, realised this aim. "In most cases, the radiocarbon levels deduced from marine and other records have not been too far wrong. However, having a truly terrestrial record gives us better resolution and confidence in radiocarbon dating," said Bronk Ramsey. "It also allows us to look at the differences between the atmosphere and oceans and study the implications for our understanding of the marine environment as part of the global carbon cycle."[50]