2. STOCK-BASED COMPENSATION - Compensation costs (Details) - USD ($) $ in Thousands	3 Months Ended
Aug. 31, 2016	Aug. 31, 2015
Stock-based compensation in the form of employee stock options, RSUs and ESPP shares included in:
Total stock-based compensation	$ 319	$ 319
Cost of Sales
Stock-based compensation in the form of employee stock options, RSUs and ESPP shares included in:
Total stock-based compensation	24	22
Selling, General and Administrative
Stock-based compensation in the form of employee stock options, RSUs and ESPP shares included in:
Total stock-based compensation	247	238
Research and Development
Stock-based compensation in the form of employee stock options, RSUs and ESPP shares included in:
Total stock-based compensation	$ 48	$ 59

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.F)
-URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5047-113901

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(1)(i)
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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