My stock on hand figure is not matching what is in Katana - why?

By default, the on-hand figure in StockTrim is the current on hand MINUS your allocated stock, since that is what is most relevant for your future stock requirements. 

If you don't want to still include allocated stock in your current figure, then under settings enable the "Include allocated stock in on hand values" setting. This is not recommended however, since stock that is already allocated will be treated by the system as available, therefore reducing your recommended future orders, so you may be cut short of stock in the future.