Let’s start with a little background on what TPO charts, and where the letters and numbers came from that make up the TPO Profile charts. On the trading floor, when the traders were in the pit and they had a trading card, each half-hour was called a bracket and when they traded, they would have to write down the letter of the bracket that the trade occurred in. So, each letter was very specific to a half-hour time frame and that's how the letters became the building blocks for the TPO charts.