Extra shift depreciation allowance defines eligibility, exclusions, and calculation method for double and triple shift operations. Normal depreciation rules changed from 1970-71: before 1970 non-seasonal factories' depreciation depended on days worked and seasonal factories required working all seasons for full allowance; from 1970-71 normal depreciation is fully admissible if a factory worked at any time in the previous year. Extra shift depreciation is additional to normal depreciation, claimable only on proof of actual double or triple shift working, excludes plant marked 'NESA' and certain categories, uses a 180-day (seasonal) or 240-day (non-seasonal) norm (or actual days if greater), and is calculated by specified formulae for double (half normal depreciation proportionate to double-shift days) and triple shifts (full normal depreciation proportionate to triple-shift days).