Abstract: A thermal head comprises a substrate with a folding line, a first thermal resistor dot line formed on a first side of the substrate in a first density of dots, a second thermal resistor dot line formed on a second side of the substrate in a second density of dots different from the first density, and wiring lines for the first and the second thermal resistor dot lines. The substrate is folded along the folding line to form a dihedral angle.

Abstract: An ink jet system printer of the charge amplitude controlling type includes a print control system for emitting printing ink droplets provided for forming a matrix pattern and interpolation ink droplets interposed among the printing ink droplets at a ratio, for example, 1/20. A counting system is provided for counting the number of printing ink droplets while a printer head travels a predetermined length. The counted number is compared with a reference number. In response to the comparison result, the interpolation dot ratio is varied in order to compensate for the variation of the travelling speed of the printer head.