Something very exciting is happening tomorrow in the world of metrology -- not meterology, the science of weather, though that is fascinating, too -- the vote to change the definition of the kilogram. Pray tell Phil, what are you yammerin' about? You see, the standard for the kilogram is defined by a cylinder of platinum-iridium forged in 1879, stored just outside of Paris in a vault under lock and key and has a mass of exactly one kilogram. If you want to verify that you have exactly one kilogram of something you bring it Versailles and ask them to weigh your object against Le Grand K, as the cylinder is known. Okay, but what is that measured against? Ah, there's the rub. Originally the kilogram was the mass of one litre of frozen water. So you see the problem of infinite regression. The other problem is that hunk of metal can be more or less a kilogram if just one atom absorbs something from the air or a few electrons are released. Better to have standard based on some universal constant like the speed of light, or time, or in the kilograms case, Planck's Constant (the value of the energy in a photon of light divided by its wavelength). So all you need is something called a Kibble balance and, voilà, you can redefine a kilogram. It's a little more mathy than that but I quibble. So, let's go for one last Utata Thurday Walk before the kilogram is redefined! Tag your photos with utata:project=tw656 and post one small image in this thread.