Check a payroll run against the last one before approval

Compare this period's payroll with the last one and list every difference that needs a check, for {{approver}} to review before approving the run. The goal is to catch errors (a missed leaver, a wrong rate, an overtime typo, a duplicate payment) before money leaves the account.

Last period's payroll register (employee or ID, hours, rate, overtime, gross pay, deductions, net pay):
"""
{{previous_register}}
"""

This period's payroll register, in the same layout:
"""
{{current_register}}
"""

Known changes this period (new starters, leavers, pay rises, bonuses, unpaid leave): {{known_changes}}
Our threshold for a change worth checking: {{threshold}}

Produce:
1. Totals: gross pay, total deductions and net pay for each period, and the difference, with the calculation shown.
2. Changes by person: a table with the columns Employee, What changed, Last period, This period, Difference, Explained by a known change (yes, no, or contradicts it). Include everyone who appears in only one register.
3. Needs checking: changes above the threshold that the known changes do not explain or that contradict them, ordered by the amount that could be wrong, each with the question to ask, for example "Overtime went from 4 to 40 hours; is 40 correct, or a typing error for 4.0?" Include any person or payment that may be duplicated.
4. Arithmetic checks: lines where gross pay cannot be explained by the hours, rates and any overtime premium shown, or where gross minus deductions does not match net pay. For salaried staff, compare with last period instead. If the overtime premium is not shown, say so once rather than flagging every overtime line.

Rules:
- Use only the figures in the registers. Do not judge whether tax or benefit deductions are correctly calculated, because that depends on rules and elections not given here; flag large changes in them as questions for the payroll provider or accountant.
- Refer to people only by the name or ID in the registers, and do not comment on anyone's pay level.

Keep the text outside the tables under 200 words. If the two registers use different layouts, or someone appears under two IDs, say so at the top and match lines only where you are sure.