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Summary of significant accounting policies (Tables)
 12 Months Ended
Dec. 31, 2018
Property, plant and equipment
Office premises 47 to 51 years
Leasehold improvements over terms of the leases or the useful lives whichever is less
Furniture, fixtures and office equipment  3 to 5 years
Motor vehicles 4 years
Testing equipment   3 years
ZHEJIANG TIANLAN  
Property, plant and equipment
Land use right    Over terms of the leases
Office premises       47-50 years, with 5% residual value
Leasehold improvements   over terms of the leases or the useful lives whichever is less, with 5% residual value
Plant and machineries     5 to 10 years, with 5% residual value
Furniture, fixtures and office equipment              3 to 5 years, with 5% residual value
Motor vehicles    1 to 8 years, with 5% residual value