The manager of a local grocery store is having dinner with his statistician friend. The store manager tells his friend about a certain cashier who is stealing from the company.

The manager is frustrated because he thinks he knows who the thief is, but can’t fire the miscreant because the employee has been with the company for years and is well-liked by customers, and neither the manager nor corporate accounting has ever actually caught this employee stealing.

At the end of each shift, each register is reconciled. The corporate rule is that any underage greater than $15 or overage greater than $10 causes an investigation. It’s common for a register to exceed these limits, but these triggers have never raised suspicion around the suspected thief. The manager’s hands are tied.

The store has eight cash registers and 12 cashiers. No more than eight cashiers work on a given day.

The statistician says that if the manager will provide 10 days worth of reconciliation records, the thief can be found. The data below are what the manager provides.

Which employee is the thief? The answer can be found using a single time-ordered chart and solidified with a little added deduction.

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