A writing pen capacitively detects and amplifies signals generated by a writing table that produces a varying electrostatic field near its writing surface. The pen cartridge, which senses the signal, is capacitively coupled to a concentric electrode, from which the signal which has been detected may be obtained for amplification.

A portable hand-held length probe with a length measuring wheel and a tracing unit which is mounted adjacent the wheel and is movable by pressing the tracing unit against a surface to be measured. A wheel movement indicative output signal is effected as function of wheel movement, and the probe carries a switch which is actuated as a function of depress-release movement of the tracing unit to enable or disable transmission of the wheel movement indicative output signal.

A pen status indicating system for a digitizer pen utilized in conjunction with a digitizer having a grid of spaced conductors positioned beneath a writing surface. The digitizer includes an electronic system which scans the spaced conductors and senses signals produced in the spaced conductors by a transmitting coil located near the writing tip of a pen used to write on the writing surface. The pen status indicating system senses whether the writing tip of the pen is pressed against the writing surface. The pen status indicating system includes a split inductor having a movable core coupled in direct communication with a pen cartridge having the writing tip connected thereto. When the pen is raised, the movable core occupies a first position relative to the secondary winding of the split inductor windings and when the pen is lowered, the movable core is caused to occupy a second position relative to the split inductor windings, causing a phase reversal in a signal produced on a center tap conductor of the split inductor. A sensing circuit including a phase sensitive detector, a filter, and a comparator produces a pen status output signal in response to the signal on the center tap conductor.

First and second switches, which are to be operated by a user, are provided on a pen-shaped housing. A first heat generating head for writing an image on a rewritable heat sensitive sheet is arranged at an end of a tapered end portion of the pen-shaped housing, and a second heat generating head, for generating heat at a temperature which is different from a temperature of heat generated from the writing head, is arranged at flat another end of the pen-shaped housing. The writing head generates heat only when the first switch is turned on, and the erasing head generates heat only when the second switch is turned on, so that the erasing head erases the image which have been written on the heat sensitive sheet from the sheet.

A digitizing stylus which generates a pulse that is not dependent upon the spatial displacement of the contacting pin, embodied in accordance with the invention so that the toroid coil can be moved axially, together with the contacting pin. This preferably is attained by providing that the contacting pin and the toroid coil are integrally cast in plastic, and the plastic body thereby formed has an extension on its inner end which extends to interconnect with an actuation body that is held within the shaft of the digitizing stylus, in an axially movable manner. Excitation of the toroid coil is triggered by the displacement of the actuation member, and a constant amplitude pulse will occur because no movement occurs between the contact pin and the toroid coil.