Bodycote uses various APMs, in addition to those reported under IFRS, as management believe these measures enable users of the financial statements to assess the underlying trading performance of the business. The APMs used include headline operating profit, return on sales, headline profit before taxation, EBITDA, headline EBITDA, headline tax rate, headline earnings per share (EPS), headline operating cash flow, free cash flow, headline operating cash conversion, net cash and return on capital employed (ROCE). These measures reflect the underlying trading performance of the business as they exclude certain non-operational items, acquisition costs and amortisation of acquired intangible assets. The Group also uses revenue growth percentages adjusted for the impact of foreign exchange movements, where appropriate, also to better represent the underlying performance of the business. The measures described above are also used in the targeting process for executive and management annual bonuses (headline operating profit, operating cash-flow) and share schemes (headline operating profit, headline operating cash flow, headline EPS).

The constant exchange rate comparison uses the current year reported segmental information, stated in the relevant functional currency, and translates the results into its presentational currency using the prior year's monthly exchange rates. Expansionary capital expenditure is defined as capital expenditure invested to grow the Group's business.

APMs are defined and reconciled to the IFRS statutory measure as follows:

Headline operating profit

2018
£m
2017
£m
Statutory operating profit134.1119.4
Add back:
Amortisation of acquired intangibles3.74.5
Acquisition costs0.5
Headline operating profit138.3123.9

Return on sales

2018
£m
2017
£m
Headline operating profit138.3123.9
Revenue728.6690.2
Return on sales19.0%18.0%

Headline profit before taxation

2018
£m
2017
£m
Profit before taxation132.2117.0
Add back:
Amortisation of acquired intangibles3.74.5
Acquisition costs0.5
Headline profit before taxation136.4121.5

EBITDA and Headline EBITDA (Earnings Before Interest, Taxation, Depreciation, and Amortisation)

2018
£m
2017
£m
Operating profit134.1119.4
Depreciation and amortisation65.764.3
Impairment of fixed assets1.80.4
Profit on disposal of property, plant and equipment(1.7)(0.7)
Loss on disposal of businesses0.6
Share-based payments3.87.8
EBITDA204.3191.2
Acquisition costs0.5
EBITDA and Headline EBITDA204.3191.2

Headline tax rate

2018
£m
2017
£m
Headline tax charge29.527.8
Headline profit before taxation136.4121.5
Headline tax rate21.7%22.9%

Headline tax charge excludes tax on amortisation of acquired intangibles and US tax reform impact in 2017: £0.9m (2017: £8.1m).

Headline earnings per share A detailed reconciliation is provided in note 8.

Headline operating cash flow

2018
£m
2017
£m
Cash generated by operations197.8182.8
Less:
Net capital expenditure(74.0)(74.8)
Add:
Restructuring cash flows4.43.7
Acquisition costs0.5
Headline operating cash flow128.7111.7

Free cash flow

2018
£m
2017
£m
Cash generated by operations197.8182.8
Less:
Net capital expenditure(74.0)(74.8)
Financing costs(1.9)(2.1)
Taxation(24.5)(22.9)
Free cash flow97.483.0

Headline operating cash conversion

2018
£m
2017
£m
Headline operating cashflow128.7111.7
Headline operating profit138.3123.9
Headline operating cash conversion93.0%90.2%

Net cash

2018
£m
2017
£m
Cash and bank balances38.541.0
Bank overdrafts (included in borrowings)(2.3)(1.4)
Net cash36.239.6

Return on capital employed

2018
£m
2017
£m
Headline operating profit138.3123.9
Average capital employed*673.4642.5
Return on capital employed20.5%19.3%

* Capital employed is defined as net assets adjusted for net cash/(debt)

Revenue and headline operating profit at constant exchange rates

Reconciled to revenue and headline operating profit in the table below:

Year to 31 December 2018
ADE
£m
AGI
£m
Central
cost and
eliminations
£m
Consolidated
£m
Revenue288.0440.6728.6
Constant exchange rates adjustment4.03.77.7
Revenue at constant exchange rates292.0444.3736.3
Headline operating profit68.782.4(12.8)138.3
Constant exchange rates adjustment1.00.41.4
Headline operating profit at constant exchange rates69.782.8(12.8)139.7