Other kinds of welding. Some kinds of welding do not use an electric arc. They might use a flame, electricity without an arc, an energy beam, or physical force. The most common type of welding that does not use an arc is called gas welding.
TDW - Total Diamond Weight. A term usually used when there is more than one diamond in a particular piece of jewelry. The combined weight of all of the (diamond) stones.
Difference between ppm and EC. Total Dissolved Solids (TDS) is the best measurement of the nutrient concentration of a hydroponic solution. To estimate TDS, one can use a meter that measures the Electric Conductivity (EC) of a solution, and convert the number to TDS in parts per million (ppm). Many meters will do this conversion.