1. A handheld device, comprising: inertial sensors comprising a gyroscope that generates gyroscope data representing a trajectory of a movement of the handheld device and an accelerometer that generates accelerometer data representing a tilt of the handheld device relative to earth's gravity; and a processing component that: determines the trajectory of the movement of the handheld device by combining the gyroscope data representing the trajectory of the movement of the handheld device and the accelerometer data representing the tilt of the handheld device relative to earth's gravity; converts, via a training mode, a first portion of the data into a first set of values corresponding to a first plurality of discrete features, associates the first set of values with a character, stores the first set of values and information representing the character in a training database, converts, via a recognition mode, a second portion of the data into a second set of values corresponding to a second plurality of discrete features, wherein a discrete feature of the first plurality of discrete features or the second plurality of discrete features includes at least one of an angle of the trajectory, an inverse tangent of a change in a pitch associated with the movement divided by a change in a yaw associated with the movement, a location of a crossing point associated with the character, or a number of times in which the trajectory changes direction; and in response to a determination that the second set of values matches the first set of values with respect to a defined condition, displays the character.