In the equity world, where there are thousands of stocks, I prefer to scale by adding fresh new positions vs adding to existing ones. I find that a fresh new signal has more potential then adding to an existing signal that is slowly fading in strength. This means that over time, as the market stays stronger, you will have more and more exposure. When the market weakens, you will automatically have less exposure. It's self adjusting. You will have your largest exposure when the market is at it's strongest and your least exposure when the market is at it's weakest.