mass", etc. In a different gravitational field, for example, on the surface of the Moon, an object can have a significantly different weight than on Earth. The gravity on the surface of the Moon is only about one-sixth as strong as on the surface of the Earth. A one-kilogram mass is still a one-kilogram mass (as mass is an intrinsic property of the object) but the downward force due to gravity, and therefore its weight, is only one-sixth of what the object would have on Earth. So a man of mass 180 pounds weighs only about 30 pounds-force when visiting the Moon. SI units In most modern scientific work, physical quantities are measured in SI units. The SI unit of weight is the same as that of force: the newton (N) – a derived unit which can also be expressed in SI base units as kg⋅m/s2 (kilograms times metres per second squared). In commercial and everyday use, the term "weight" is usually used to mean mass, and the verb "to weigh" means "to determine the mass of" or "to have a mass of". Used in this sense, the proper SI unit is the kilogram (kg). As of 20 May 2019, the kilogram, which is essential to evaluate the weight of an object, has been redefined in terms of Planck's constant. The new definition does not affect the actual amount of the material but increases the measurement's quality and decreases the uncertainty associated with it. Prior to using Planck's constant, a physical object was used as a standard. The object, located in a vault in Sèvres, France, has fluctuated by approximately 50 micrograms of its mass since it was first introduced in 1889. Consequently, the following must be true. Mass, which should be the same whether on earth or the moon for example, is only valid on earth since it needs to be referenced. Also, comparing a weight measurement to a standard that changes with time cannot be used as a reference without citing the actual value of it at the time and moment it was used as such. Therefore, to redefine the kilogram all National Metrology Institutes (NMIs) involved determined the new value of Planck's constant by evaluating a mass which was calibrated against the IPK. To this extent one kilogram is equal to h/(6.62607015×10^(-34) ) m^(-2) s which equals 1 m^(-2) s. A kilogram has remained the same quantity