The METAS watt balance project was initiated slightly more than a decade ago. Over this time, the apparatus has been through an uninterrupted series of upgrades that have improved its reliability to a point where continuous series of measurements can be taken fully automatically over periods of several months. A comprehensive analysis of possible systematic errors has now been completed and a large set of data has been analysed to calculate a value for the Planck constant h. This paper describes the watt balance in detail, explains the data acquisition and analysis thoroughly and presents the uncertainty budget. The value of the Planck constant determined with our apparatus is h = 6.626 069 1(20) × 10−34 J s with a relative standard uncertainty of 0.29 × 10−6. This value differs from the 2006 CODATA adjustment by 0.024 µW W−1.

Among the priority tasks in the further development of the International System of Units is the redefinition of the kilogram based on fundamental constants. One of the strategies pursued today is to relate mass to Planck's constant h using the equivalence between mechanical and electrical energies. In this paper, possible experimental approaches in this direction are described. The approach which promises to reach the required uncertainty at the earliest is the concept of the moving-coil watt balance. The status of the different watt balance experiments is reviewed in detail.

A method is presented that can be used for the evaluation of the value of the Earth gravity field at any defined position inside or outside an instrument used for physical or metrological experiments. After a brief presentation of the gravimeters used and the evaluation of their respective uncertainties, we describe in detail the procedure developed to determine the gravitational acceleration g at the point of interest. Finally, a realistic evaluation of the uncertainty budget shows that the method can be used in many metrological applications and especially in all experiments aiming at a new definition of the kilogram by virtual comparison of mechanical and electromagnetic power.In this paper, we denote with g the Earth gravity field or gravitational acceleration, which is the sum of all accelerations felt by a free falling body at the surface of the Earth.

The new definition of the kilogram, which is expected to be adopted by the General Conference on Weights and Measures in 2018, will bring some major changes to mass metrology. The most fundamental change will be the replacement of the present artefactbased definition with a universal definition, enabling in principle any National Metrology Institute (NMI) to realize the kilogram. The principles for the realization and dissemination of the kilogram in the revised SI are described in the mise en pratique of the definition of the kilogram. This paper provides some additional information and explains how traceability can be obtained by NMIs that do not operate a primary experiment to realize the definition of the kilogram.

The redefinition of the kilogram, expected to be approved in the autumn of 2018, will replace the artefact definition of the kilogram by assigning a fixed numerical value to a fundamental constant of physics. While the concept of such a change is pleasing, the mass community as represented by the Consultative Committee for Mass and Related Quantities (CCM) was faced with a number of technical and procedural challenges that needed to be met in order to profit in any meaningful way from the proposed change. In the following, we outline these challenges and how the CCM has met and is meeting them. We focus especially on what the mass community requires of the new definition and the process by which the CCM has sought to ensure that these needs will be met.

A b stractT h e Altdir group is currently designing an objectorien ted d ata base sy stem called 0 2 T h is paper presents a form al description of the ob ject-orien ted d ata m odel of th is system . It proposes a typ e system defined in the fram ework of a set-an d -tu p le d a ta m odel. It m odels the w ell know n inheritance m echanism and enforces strong typing. IntroductionOne of the o b jectiv es of th e Altdir G roup is to develop a new gen eration d atab ase system . T h e targ et app lication s are tradition al b u sin ess app lication s, transaction al appli cations (exclu d in g very high perform ance applications), office au tom ation and m u lti-m ed ia applications. T he sy stem w e are d esigning is object-oriented. W e briefly recall th e m ain featu res of th e object-oriented paradigm : (i) O b ject id en tity. O b jects h ave an existen ce w hich is in d ep en d en t of their value. T hus, tw o ob jects can be either id entical, th a t is, th ey are th e sam e object, or th ey can be equal, i.e., th ey have th e sam e value. (ii) T h e n otion of type1. A typ e describes a set of ob jects w ith th e sam e characteristics. It describes the struc ture of d a ta carried b y ob jects as w ell as th e opera tio n s (methods in th e ob ject-orien ted term inology) applied to th ese objects. U sers of a typ e only see the in terface of th e typ e, th a t is, a list of m eth odsPermission to copy without fee all or part of this material is granted provided that the copies are not made or distributed for direct com mercial advantage, the ACM copyright notice and the title of the publication and its date appear, and notice is given that copying is by permission of the Association for Computing Machinery. To copy otherwise, or to republish, requires a fee and/or specific permission. © 1988 A C M 0 -8 9 7 9 1 -2 6 8 -3 /8 8 /0 0 0 6 /0 4 2 4 $1.50 togeth er w ith their sign atu res (th e typ e of the input param eters and the typ e of the result): th is is called

In this paper, we present a type model for objectoriented databases. Most object-oriented databases only provide users with flat objects whose structure is a record of other objects. In order to have a powerful expression power, an object-oriented database should not only provide objects but also complex values recursively built using the set, tuple and disjunctive constructors. Our type model presents two notions: that of classes whose instances are objects with identity and that of types whose instances are complex values. The two notions are mixed in that an object is modeled as a pair containing an identifier and a value, and a value is a complex structure which contains objects and values. We define in this context the notions of subtyping and provide a set inclusion semantics for subtyping.

The further development of the International System of Units and the redefinition of the mass unit based on a fundamental constant is a priority task of the metrology community. Two main strategies are pursued today, counting atoms and relating mechanical to electrical power. In this article the actual status of the kilogram and the different proposed methods are reviewed.