Income derived from employment sourced in Hong Kong is taxable in Hong Kong. The source of employment is laid down in the Goepfert Rules and Departmental Interpretation and Practice Note No.10. However, those individuals who visit Hong Kong for periods not exceeding 60 days will be exempt from paying Salaries Tax. This provision is known as the "sixty-day rule". Employment sourced in Hong Kong will be fully chargeable to Salaries Tax whereas offshore employment will be chargeable on a "time-in-time-out" basis, the taxable income of which will be apportioned by reference to the days present in Hong Kong. Employment of a government civil servant is considered sourced in Hong Kong and therefore its income is always fully taxable in Hong Kong.