14 Trade accounts receivable

CHF 1,000	2013	2014
Trade accounts receivable
Denominated in CHF	19,684	32,715
Denominated in EUR	20,538	20,303
Denominated in GBP	1,437	1,213
Denominated in USD	28,743	32,800
Denominated in JPY	1,035	2,625
Denominated in other currencies	4,486	8,302
Subtotal trade accounts receivable	75,923	97,958

Allowance for doubtful accounts
Individual impairment allowance account	(1,501)	(1,542)
Collective impairment allowance account	(38)	(233)
Subtotal allowance for doubtful accounts	(1,539)	(1,775)

Construction contracts in progress
Aggregate amount of cost incurred and recognized profits	476	2,721
Amounts of advances received	(208)	(955)
Subtotal construction contracts in progress	268	1,766

Balance at December 31	74,652	97,949

(Decrease) /increase	(6,538)	19,651
Acquisition through business combination	–	1,261
Translation differences	(1,202)	2,385
Total change compared with previous year	(7,740)	23,297

Amount of contract revenue recognized as sales in the statement of profit or loss relating to construction contracts	6,842	7,661

The maximum exposure to credit risk for trade accounts receivable at the reporting date by geographic region was:

CHF 1,000	2013	2014
Switzerland (domestic)	3,645	2,549
Euro-zone countries	23,289	33,562
Other European countries	3,358	6,695
North America	34,385	39,901
Asia	9,286	11,998
Other	1,960	3,253

Balance at December 31	75,923	97,958

The Group’s most significant customer accounts for 10.4% of the trade accounts receivable carrying amount at December 31, 2014 (December 31, 2013: 6.1%).

The movement in the allowance for impairment in respect of trade accounts receivable during the year was as follows:

CHF 1,000	2013	2014
Individual impairment allowance account
Balance at January 1	(2,152)	(1,501)
Change in impairment losses	596	(8)
Write-offs	45	5
Translation differences	10	(38)

Balance at December 31	(1,501)	(1,542)

Amount of trade accounts receivable with individual impairment (gross)	1,918	1,839

Collective impairment allowance account
Balance at January 1	(58)	(38)
Change in impairment losses	21	(193)
Translation differences	(1)	(2)

Balance at December 31	(38)	(233)

The due dates of trade accounts receivable that are not individually impaired were:

	2013		2014
CHF 1,000	Gross	Impairment	Gross	Impairment
Not past due	61,703	(25)	49,680	(28)
Past due 1 – 30 days	7,738	(11)	40,549	(7)
Past due 31 – 90 days	4,234	(2)	5,355	–
Past due 91 – 360 days	228	–	516	(196)
Past due more than one year	102	–	19	(2)

Balance at December 31	74,005	(38)	96,119	(233)

The Group did not experience any severe financial difficulties with its debtors in the past. The sum of all recognized final write-offs of trade accounts receivable in 2013 and 2014 represents less than 1% of sales.