IDEA INC <IDEA> TO BUY PRIVATE FIRM IDEA Inc said it signed a letter of intent to buy privately-held Structural Instrumentation Inc. The purchase, for an undisclosed sum, will be made mostly with IDEA common stock, the company said. IDEA said the purchase will add about 32 cts per share to its fiscal 1988 earnings. IDEA reported earnings of four cts per share for the quarter ended October 31, 1986.