gular position and motion of the shaft/axle to digital codes and transmitted information at frequency of five times per second. Serial data of the heights of the table top, back section, leg section, and other components along with the angle data of the horizontal and vertical rotations were collected. These data were transferred to the display software (M72D10) installed in a personal computer (PC) connected to the operating table. All position data were recorded and saved as a separate file. The measurement errors of data from each encoder were estimated within ± 2 mm for section height and within ± 4 degree for angles. This recorded data would be considered as a reference for position of the same or another patient in future operations, which could be displayed as green color illustrations in the same screen simultaneously ([Figs. 2c](#F2){ref-type="fig"}, [3d](#F3){ref-type="fig"}). Displayed body position would be corrected if it did not coincide with the previously recorded data of the same position or at the surgeon's discernment. In addition, the side and the front views of the operating table could be displayed in schematic images. They were displayed either as parallel lines or oblique lines in the form of cabinet drawing. The oblique lines were along a line that would intersect the Y-axis (head-clamp axis) at an angle of 30 degrees ([Fig. 2d](#F2){ref-type="fig"}). This angle could be changed from 0 degree to 90 degrees.

The central point of the head (intersection of the mid-sagittal plane with inter-meatal line) and the position of the heart (right atrium) were recorded for each case. As a result, characteristics of the operating table and the position of the heart and the head could be displayed on an external monitor. The spatial relationships between the reference points could be determined by drawing vertical lines from the central points of the head and the heart towards the back section of the operating table. The flashing frequency of the heart position indicator was once every 5 data collec