The height was formerly shown on
Ordnance Survey maps as 609 metres. The closeness of this figure to the threshold of used in the
United Kingdom to separate mountains and hills led to the summit being surveyed using precision
GPS and levelling equipment. The height was found to be 609.58 ± 0.1 m, or fractionally below 2,000 feet. The result was discussed with the authors of the
Nuttalls,
Hewitts and
Deweys who all agreed that the hill should retain its current status as a member of Dewey's list of hills at least 500 metres but less than 609.6 metres high. Current OS maps show the height rounded to 610 metres. The Ordnance Survey recalculated the height of the mountain in 2016 when the authoritative definition of the
British national height datum,
Ordnance Datum Newlyn, was transitioned from the OSGM02
geoid model to the OSGM05 version, causing a general upwards shift of 25mm in
orthometric heights. This resulted in a height of 609.606 metres, thus updating the status of Calf Top from hill to mountain. ==References==