THE CRISIS: A Telltale Tape Deepens Nixon's Dilemma

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Executive Office Building to agree on their procedures. "I've done almost nothing else for two months," he said, estimating that the panel had spent up to 300 man-days examining the tape variously in Manhattan, Cambridge, Salt Lake City, New Haven, Murray Hill, N.J., and Los Gatos, Calif. They were supplied with the now-celebrated Uher 5000 tape recorder used by Rose Mary Woods for transcribing subpoenaed tapes, another White House Uher recorder for comparison, as well as Miss Woods' lamp and typewriter.

Picking up a pointer, Bolt explained a large chart that presented the panel's findings in graphic form. A principal technique used in arriving at their conclusions, he noted, was to develop the tape "in a sense that you develop a picture." A fluid containing magnetically sensitized particles was rubbed over the tape. The particles arranged themselves in conformity to magnetic imprints previously induced on the tape by electronic signals in the original recording and erasing processes. Thus the imprints could be seen with the naked eye and photographed. Bolt also noted that the signals had been analyzed by oscilloscope, fed through frequency spectra devices, and put into digital computers. Seventy minutes of the tape, which also contained a non-Watergate conversation between Nixon and John Ehrlichman, former Domestic Affairs Adviser, had been played back for listening.

The Signature. Speaking animatedly and in a high-pitched voice, Bolt explained the rudiments of a tape recorder's operation. When the "record" and "start" buttons are pushed, the tape rolls past two "heads" containing tiny electromagnets. The first, the erase head, eliminates most previous signals on the tape. The second, the record head, implants new signals. On the Uher, the two heads are "rigidly fixed" at 28.6 mm. apart. When the erase head is released on the Uher (but not on all recorders) it leaves a minute but discernible four-line "signature" on the tape. This mark is distinctive to the machine. When the machine is set to begin recording, the record head also leaves a distinctive mark.

Another of the experts, Thomas G. Stockham Jr., a computer-science professor at the University of Utah, then cheerily demonstrated that once the record button is depressed, it "locks itself down." It can be released only by pushing any of four other buttons: "start," "fast forward," "rewind" or "stop." If a foot pedal is used to control the recorder, the lifting of a foot will cause the tape to stop moving, but will not result in the erase head's leaving the telltale four-line "off' signature.

When they developed the 18-minute segment of tape, the experts found five of the "off' signatures, indicating that while the record button was down, it had been manually released at least five times by pushing other buttons. Each of these "off' signatures was preceded on the tape, logically enough, by an "on" mark. That meant that someone had pushed three buttons (two to start, one to stop the erase-record process) at least five times (see chart).

Actually, the experts are almost certain that nine such operations were involved. This is because they discovered four other "on" marks. The only reason they did not declare