| Accounts receivable |
Accounts receivable consist of the following at: | | | | | | | | | | | January 31, 2016 | | July 31, 2015 | Billed receivables from commercial customers | | $ | 27,677,000 |
| | 39,062,000 |
| Billed receivables from the U.S. government and its agencies | | 15,124,000 |
| | 8,375,000 |
| Unbilled receivables on contracts-in-progress | | 12,629,000 |
| | 23,024,000 |
| Total accounts receivable | | 55,430,000 |
| | 70,461,000 |
| Less allowance for doubtful accounts | | 1,681,000 |
| | 1,206,000 |
| Accounts receivable, net | | $ | 53,749,000 |
| | 69,255,000 |
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