Euromet project 691

1. Euromet project 691 Calibration Inter-comparison of a 5-litre volume glass standard P. Lau

2. Task: ”Perform a volume calibration!” • How many laboratories? 20 from 19 countries • Which volume? ”dry, contained” – below the mark • ”wet, delivered or poured” • How many measurements? • contained 18 labs: 4(1 lab)8(1 lab) 10 (14 lab)11 (1 lab) 15 (1 lab) • delivered 16 labs: 15 (3 lab)10(13 lab) • 15 laboratories performed both calibrations • What about cleaning? no instructions given • Pouring times? according to laboratory practice • How to report uncertainty? form but no instructions given

3. Result ”contained” or ”dry” volume  0,01 % mean  2 s median  0,13 ml  1,1 ml 10 measurements 11 4 8 15

4. Result “delivered”, “wet” or ”poured” volume  0,01 %  0,16 ml mean  2 s median  1,1 ml 15 15 15 10 measurements

5. Uncertainty (k=2) – range and standard deviation GUM GUM Poland PTB PTB Germany Uncertainty BNM - LNE France BNM - LNE Range IPQ Portugal IPQ Stdev OMH Hungary OMH NMI Bulgaria NCM IMGC Italy IMGC Slovak Rep. SLM SLM Switzerland METAS METAS Netherlands NMi NMi United Kingdom NWML NWML Turkey UME UME Belgium SMD SMD Denmark FORCE FORCE Austria BEV BEV Uncertainty Sweden SP SP Range Czech Rep. CMI CMI Stdev Slovak Rep. SMU SMU Greece EIM EIM Spain CEM CEM 0 0 , 2 0 , 4 0 , 6 0 , 8 1 , 0 1 , 2 0 0 , 2 0 , 4 0 , 6 0 , 8 1 , 0 ”contained” volume ”delivered” volume ml ml

6. Distribution of uncertainty components 1-sigma level 1,10 weighing 1 weighing 2 stdev water density 0,70 meniscus water density weighing 1 weighing 2 0,53 stdev water density air density weighing 0,46 meniscus stdev weighing water density 0,46 meniscus stdev water density weighing 0,45 meniscus water density stdev weighing 0,42 0,38 meniscus temperature stdev water density komp. 1 0,37 stdev weighing water density temperature komp. 2 0,35 meniscus temperature water density stdev komp. 3 0,35 komp. 4 stdev meniscus water density weighing 0,35 stdev water density temperature weighing 0,31 * stdev weighing water density meniscus 0,29 stdev water density air density weighing 0,26 stdev meniscus water density weighing 0,22 meniscus stdev weighing temperature 0,22 stdev water density air density weighing 0,16 * meniscus stdev water density weighing 0,14 weighing water density stdav meniscus 0,13 stdev temperature weighing 1 weighing 2 U(contained volume) * values for GUM & PTB refer to delivered volume

7. Cross-correlation – “degree of equivalence” ±2 s area CMI BNM-LNE SMU SLM PTB GUM

8. Uncertainty declaration • Just one figure – Force (1) • 5 components – SMD, NWML (2) • 6 components – Metas, UME (2) • 7 components – IPQ, BNM-LNE, SMU, NMi, BEV (5) • 8 components – CMI, SLM, CEM, OMH (4) • 9 components – SP, GUM, NCM (3) • 11 components – EIM (1) • 14 components – PTB (1)

9. Possible conclusions from the • The total outcome is satisfactory. • One lab out of 20 (5 %) (in 35 results) just outside 95 % confidence level. • Large difference in repeatability between the laboratories (is low spread always good?). • Large difference in uncertainty declarations. • Some results (at least 5 for dry and 6 for wet volume) are unrealistic small. • Probably 3 to 5 components really matter. • A good and realistic uncertainty estimation depends more on a ”feeling” than on a sophisticated modelling. • In the perspective of an inter-comparison systematic effects (connected with a method) are serious uncertainty contributions (cleaning, pouring, experimental realization). • The meniscus setting is very personal (random within laboratory – systematic in global aspect). • In my opinion uncertainty declarations need to incorporate the limitations of a calibration object.