25 and the first side plate 15 a first end of the resilient member 32 is located in the sliding slot 251 the securing portion 311 is engaged in the locking hole 151 the resilient member 32 slips over the securing portion 311 and abuts the blocking portion 312 the securing member 31 is rotated towards the bracket 10 to elastically deform the resilient member 32 the resilient member 32 exerts elastic force to engage the sliding ruler 20 to the bracket 10 and prevent the sliding ruler from moving towards the first side plate 15 in use the base 11 of the bracket 10 is placed on a ground the measuring device determines a plurality of positions having different pre setting distances from the ground when the different pre setting distances are smaller than or equal to the scale value n the first set of scale lines and the second set of scale lines of the bracket 10 is capable of measuring the different pre setting distances and determine the plurality of positions when the different pre setting distances are greater than the scale value n the securing member 31 is rotated away from the first side plate 15 the resilient member 32 rebounds to release the sliding ruler 20 the gear 53 is rotated to slide upwards the sliding ruler 20 until the third scale value and the fourth scale value are equal to each pre setting distance the securing member 31 is rotated towards the first side plate 15 the resilient member 32 is elastically deformed to engage the sliding ruler 20 to the bracket 10 thus a distance between the top wall 22 and the ground is equal to the pre setting distance thus the.