Tariff types change regularly, and the OWL +USB cannot directly accommodate a block or standing charge tariff. Utility companies cannot directly tell you which units you will use will be charged at the particular tariff. When a tariff is set for say the first 100 units at a higher price, generally they simply charge you for 100 units from your bill for the month and the rest is charged at the alternate price. If a tariff is set so that you pay so an additional standing fee every day, or every month, then that standing fee is simply added to the cost over each day or the month.
To gain a better understanding of what your electricity is costing you at any given time, it is better to spread those standing charges out across all the usage so you can see what your appliances are costing including the block or standing charges.
To do this you need to understand what the total cost is per unit. This is best done from a previous bill, or even better over several bills.
Find the total you have been charged by your Utility company for a given period
Find out how many units you have used in that period
Calculate your tariff by dividing the total cost by the number of units.
This will give you a single tariff figure somewhat higher than the lower tariff figure stated by the Utility company, and between the two figures in the case of a block tariff.
Enter this as a single tariff by following the instructions for a single tariff setting on the OWL +USB.