The ranges are average values and are exceeded by most current measuring instruments. A minimum distance of 32.8 ft (10 m) is required for some instruments. In order to guarantee accurate measurements with reflective targets the target angle should be a maximum of 30°. Survey markers with reflective targets are exclusively recommended for carrying out distance measurements using a tachymeter or total station. Survey markers with crosshairs, but without reflective targets, are available for the use of levelling instruments, theodolites and construction lasers.