Some recorders produce the record by applying a series of dots of ink to the chart. In this way not only can the development of a parameter by built up as a line but digital information can be printed across the chart.

The print heads used in these recorders are effectively a number of different coloured pens built into one body. The print head is rotated to present the appropriate colour before the head is moved to touch the paper.

Careful selection of ink is required to match the paper so that the record dries but also allows the nib to remain moist and ready to record for several months without being capped (sealed).

The body of the unit must be accurately moulded to fit the instrument and properly constructed to avoid internal migration of ink colours, which can result in some strange colour effects!