Table:
|  | Customer relationships | Brand names and trademarks | Manufacturing designs and core technology | Non-compete undertakings and other | Total acquired intangibles |
| --- | --- | --- | --- | --- | --- |
|  | £m | £m | £m | £m | £m |
| Cost: |  |  |  |  |  |
| At 1st January 2019 | 57.1 | 187.3 | 56.0 | 20.2 | 320.6 |
| Exchange and other adjustments | (3.0) | (7.8) | (2.2) | (0.9) | (13.9) |
|  | 54.1 | 179.5 | 53.8 | 19.3 | 306.7 |
| Acquisitions | 34.9 | 14.3 | 7.2 | 3.8 | 60.2 |
| At 31st December 2019 | 89.0 | 193.8 | 61.0 | 23.1 | 366.9 |
| Amortisation and impairment: |  |  |  |  |  |
| At 1st January 2019 | 25.1 | 21.3 | 14.2 | 15.6 | 76.2 |
| Exchange adjustments | (1.3) | (1.1) | (0.6) | (0.8) | (3.8) |
|  | 23.8 | 20.2 | 13.6 | 14.8 | 72.4 |
| Amortisation and impairment | 7.1 | 10.4 | 5.6 | 3.7 | 26.8 |
| At 31st December 2019 | 30.9 | 30.6 | 19.2 | 18.5 | 99.2 |
| Net book value: |  |  |  |  |  |
| At 31st December 2019 | 58.1 | 163.2 | 41.8 | 4.6 | 267.7 |
Paragraphs:
15 Goodwill and other intangible assets continued
Acquired intangibles
The disclosure by class of acquired intangible assets is shown in the tables below.
2019
Customer relationships are amortised over their useful economic lives in line with the accounting policies disclosed in Note 1. Within this balance individually material balances relate to Thermocoax £32.6m. The remaining amortisation period is 14.3 years.
Brand names and trademark assets are amortised over their useful economic lives in line with the accounting policies disclosed in Note 1. Within this balance individually material balances relate to Chromalox £114.1m (2018: £125.4m), Gestra £28.4m (2018: £32.5m) and Thermocoax £13.6m. The remaining amortisation periods are 17.5 years, 12.3 years and 19.3 years respectively.
Manufacturing designs and core technology are amortised over their useful economic lives in line with the accounting policies disclosed in Note 1. Within this balance individually material balances relate to Chromalox £12.9m (2018: £15.1m), Gestra £10.8m (2018: £12.3m) and Aflex £8.5m (2018: £9.4m). The remaining amortisation period is 12.5 years for Chromalox, 12.3 years for Gestra and 10 years for Aflex.
Non-compete undertakings are amortised over their useful economic lives in line with the accounting policies disclosed in Note 1. There are no individually material items within this balance.
Question:
What was the percentage change in the amount of individually material balances under manufacturing designs and core technology for Aflex in 2019 from 2018?
Answer: (8.5-9.4)/9.4 = -9.57