Tally System Invoices for comparison with provisional bill
When you tick this option, it will add columns to the end of the table.
There will be a column for each Meter Account that has deductions on this ledger.
For each System Invoice, there is a link in the Notes field to invoke the provisional bill for that exact date.
So you can click the link and then the Total on the Provisional Bill should match exactly the amount tallied in the Tally column.
If it does not match exactly:
1) did the tariff change since the that System Invoice was processed?
You can check this under View->Ledger Chronology
2) is the amount out by only a couple of cents?
There are different ways in which the rounding is handled.
Under Edit->Meter Account make sure Always smooth out Provisional Bills in the same way as for Prepaid is selected for all Meter Accounts used to check up on Ledger deductions. Note: Ledger deductions will always happen with rounding done in one specific way regardless of this setting, so this setting is only for comparing with Provisional Bills.

If you tick Break Bill down into separate line items and charge each one separately on the Ledger under Edit->Software Prepaid Options there will be a column tallied for every Line Item of every Meter Account.