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Absolute and Relative Uncertainty (Accuracy) in Multiphase Meter (including Wet Gas Meter)

There are a bit different regarding an uncertainty (accuracy) presentation in multiphase meter.

While in the other flow meter it is usually presented as % of calibrating span, % of span etc, 
in the multiphase meter some of its measurement result presented as relative uncertainty and 
some others in term of absolute uncertainty. For example (taken from Multiphase Vendor datasheet):
Liquid rate uncertainty: +4% relative (rel)
Water cut: +3% absolute (abs)
Gas rate: +8% relative (rel)
So what is the meaning of this relative and absolute uncertainty and why 
it is presented in these terms?
The term relative uncertainty means the percentage of the individual flow 
uncertainty which is taken from the total flow (oil + water + gas flow rate) uncertainty. 
For example,
Oil Flow Rate = 200 barrel/day
Water Flow Rate = 50 barrel/day
Gas Flow Rate = 2000 barrel/day
Total Flow Rate = 2250 barrel/day
From above data lets say the vendor specify their meter have oil, water, and gas flow 
rate uncertainty = +/-5% relative, then it means:
Oil Flow Rate Uncertainty = +/- 5%*2250 = +/- 112.5 barrel/day
Oil Flow Rate Accuracy = 112.5/200*100% = +/- 56.25%
Water Flow Rate Uncertainty = +/- 5%*2250 = +/- 112.5 barrel/day
Water Flow Rate Accuracy = 112.5/50*100% = +/- 225%
Gas Flow Rate Uncertainty = +/- 5%*2250 = +/- 112.5 barrel/day
Gas Flow Rate Accuracy = 112.5/2000*100% = +/- 5.625%
Wow, we will have a strange accuracy presentation of the oil and water flow rate and have 
a good accuracy presentation of the gas flow rate accuracy.
On the other hands, the term absolute means the percentage of the individual flow uncertainty 
taken from each individual flow rate itself. For example,
Still using oil, water, and gas flow rate above, lets say the vendor specify their meter have oil,
water, and gas flow rate uncertainty = +/- 5% absolute, then it means:
Oil Flow Rate Accuracy = +/- 5%*200 = +/- 10 barrel/day
Water Flow Rate Accuracy = +/- 5%*50 = +/- 2.5 barrel/day
Gas Flow Rate Accuracy = +/- 5%*2000 = +/- 100 barrel/day
Once again, we will have a very good presentation regarding all individual flow rate presentation. 
But usually,
 all of these good accuracy presentation can’t achieved by the vendor. Might be they can only achieved 
the oil flow rate and water flow rate accuracy but the gas flow rate accuracy 
can’t achieve by using this absolute accuracy.
As conclusion, in order to get a good accuracy presentation, the multiphase meter vendor
 usually using both relative and absolute accuracy presentation just like a multiphase meter 
uncertainty example in the beginning of this articles. This is acceptable as long as the +/- barrel/day 
derived from the specified relative or absolute accuracy is still within an acceptable limit of project or client requirements.