Generation of absolute pressure with a pressure balance is commonly done by enclosing the space above weights with a bell jar and evacuating it with a vacuum pump. Residual pressure in a bell jar is usually of the order of few tens of Pa to few Pa, depending on the effective pumping speed. Its value is added to a calculated pressure of the gravitational force of the piston and weights to obtain the generated absolute pressure. By connecting to the absolute pressure balance a precise and stable pressure gauge with sufficient resolution it is easy to observe that small changes of residual pressure in a bell jar generate a corresponding change in a pressure reading of the gauge. Unfortunately the lowest absolute pressure which can be generated by a pressure balance of conventional design is determined by the tare weight of the piston and some small additional weights necessary for sufficient minimum free rotation time and it is in the pressure range starting at 3 kPa and up to 5 kPa.

The pressure and vacuum group of the Force and Pressure Division, at the Centro Nacional de Metrologia (CENAM, Mexico) has developed two measurement systems for calibration, one for leaks and another for holes in dynamic pressure.
The leaks calibration system is based on the method of pressure increment at constant volume (and constant temperature) within the measurement range starting at 1 x 10-6 Pa·m³·s^-1 up to 5 Pa·m3·s^-1 with volumes of 0.5 L or 1 L (according to the leak range to be calibrated), with an operation pressure from 1 x 10^-5 Pa up to 130 kPa, using helium, nitrogen or air as manometric fluids.
For the calibration of holes in dynamic pressure, the method PVTt is used. This is, pressure increments at constant volume and constant temperature during a given time. The volume used is 3.75 L with a gas flow up to 20 cm³·min^-1 using nitrogen as operation fluid.
The procedure of holes calibration consists on measuring the flow through a small hole by measuring the pressure increment due to the gas accumulation in a known volume during a period of time with controlled temperature conditions. The PVTt system is formed by pressure gauges, a gas collection tank with a known volume, temperature sensors, a chronometer for time measurement, a vacuum pump, a set of valves to control the gas flow direction and the hole which will be calibrated.

The torque laboratory at the Centro Nacional de Metrología in Mexico (CENAM) started operations in 1997 with the design, built up and set up of a torque transfer standard machine for 2 kN·m (TTSM-2kN·m). Since that time, a total of five torque standards have been developed at CENAM. Two of them realize the quantity via the primary method (dead weights applied in a lever arm of a well known length) in the measuring ranges of 2 kN·m and 1 kN·m. The other three transfer standard machines are in the ranges from 20 N·m and 2 kN·m, and the last one is a TTS machine which is in the set up stage, with a range up to 20 kN·m.
This paper gives general information about the design, build up and set up of the torque standard machine up to 1 kN·m which has a dual function, this is, realizing the quantity with a primary torque standard method (PTSMe) and/or disseminating it with a torque transfer standard method (TTSMe); depending on the type of calibration one wishes to perform.

The increasing demand, in particular in Italy, for calibration and certification work and for the accreditation of new calibration centres, is due to a number of concomitant factors: The need for industry to operate in accordance with EN 45000, ISO 9000 and ISO17025 as regards quality; the Italian law 273/91 establishing the National Calibration System, which comprises the Primary Metrological Institutes and the SIT centres).
INRiM provides for traceability to the standards of mechanical, thermal and electrical quantities all over the country, so as to allow high-quality measurements and tests to be made.
At present the number of SIT centres is 194 in total, plus 24 for force quantity (load cell, testing machines, impact pendulum, torque, extensometer).
One of the most important activities of the National Accreditation Body (NAB) is the organisation of a series of interlaboratory comparisons (ILC) to verify the best measurements capability of the accredited laboratories.
One of the difficulties in the technological field is represented by the big weight and large size of the equipments to calibrate, so it is difficult or impossible to circulate such equipments (e.g. materials testing machines or impact pendulum). In this case each participating Calibration Centre has to travel to the location were the equipment is located. Another difficulty for this kind of ILC is that the object of the comparison (the Charpy Impact Pendulum - CIP) has not the status of a reference standard. For this reason in 2005 one ILC was organised in Italy for the calibration of Charpy Impact Pendulum (CIP), with the following purposes:
1. to give an experimental validation of the resilience dissemination in Italy;
2. to evaluate the calibration competence of the different laboratories;
3. to give a contribution to solve the problem for future international comparison for such kind of equipments.
Two Charpy Impact Pendulum were chosen of 500 J and 20 J rated energy, located in one Calibration Centre.
At the experimental ILC participated 6 Calibration Centres, with a grand total of more than 50 first line standards. At each laboratory was asked to calibrate the CIP by using their normal procedure (usually UNI EN ISO 10045/2). The repeatability, accuracy and classification given by each lab were compared.
The main results of the metrological evaluation of the Charpy Impact Pendulum machines obtained during the ILC are discussed.

IMEKO is a non-governmental federation of 36 national Member Organisations. The Member Organisations are scientific/technical societies or committees. They include representatives of metrological institutions, higher education institutions, industry and users of instruments.
This communication will deal shortly with the objectives of the Confederation, will inform on its structure, will highlight IMEKO imeko_proceedings and will present an overview on the activities of the 23 Technical Committees.