A method of communication between a device located in a borehole and a remote sensor, comprising the steps of: providing a drill string comprising a plurality of connected components, one or more vessels running along the drill string to form a continuous fluid path; incorporating a device into the drill string so that the device is in communication with the fluid path; inserting the drill string into a borehole so that the device is located below a surface into which the borehole is formed and the fluid path extends from the surface to the device; substantially filling the fluid path with a pressurised fluid; circulating fluid through the fluid path and through the device, so that the majority of the fluid leaves the fluid path and passes into the surrounding wellbore through an exit aperture formed below the device; providing a pressure sensor at or near the surface, the pressure sensor being adapted to sense the pressure of the fluid in the fluid path; over a communication period, restricting the flow of fluid through the fluid path at or near the device so that the resulting increase in pressure in the fluid in the fluid path can be detected by the pressure sensor: during the communication period, introducing fluid into the fluid path at a rate below 0.379 m 3 /minute [100 gallons/minute]; and following the communication period, commencing a milling or drilling operation using a milling or drilling arrangement provided as part of the drill string, wherein the exit aperture is left open during the milling or drilling operation. providing a drill string comprising a plurality of connected components, one or more vessels running along the drill string to form a continuous fluid path; incorporating a device into the drill string so that the device is in communication with the fluid path; inserting the drill string into a borehole so that the device is located below a surface into which the borehole is formed and the fluid path extends from the surface to the device; substantially filling the fluid path with a pressurised fluid; circulating fluid through the fluid path and through the device, so that the majority of the fluid leaves the fluid path and passes into the surrounding wellbore through an exit aperture formed below the device; providing a pressure sensor at or near the surface, the pressure sensor being adapted to sense the pressure of the fluid in the fluid path; over a communication period, restricting the flow of fluid through the fluid path at or near the device so that the resulting increase in pressure in the fluid in the fluid path can be detected by the pressure sensor: during the communication period, introducing fluid into the fluid path at a rate below 0.379 m 3 /minute [100 gallons/minute]; and following the communication period, commencing a milling or drilling operation using a milling or drilling arrangement provided as part of the drill string, wherein the exit aperture is left open during the milling or drilling operation. during the communication period, introducing fluid into the fluid path at a rate below 0.379 m 3 /minute [100 gallons/minute]; and following the communication period, commencing a milling or drilling operation using a milling or drilling arrangement provided as part of the drill string, wherein the exit aperture is left open during the milling or drilling operation.