what type of model is curve can ach model sales what is the purpose of a hatch model can ach be used for returns why use gap can i use garch only can a series of returns be modelled by a chart? what is the model used on a garnish can a gard model only include a return series can you use ch for a series can i use the hatch model only for a return series? when using curve can i make returns? can you use hatch to model a return series can gard be used only for return series? what is the difference between ch and ch can arc be used for return series can you use hatch model only in a return series? what model do you use to model a return series when to use garch in business what is the difference between arch and ch