Portable well diameter graduator for multi-arm sidewall contact device

The invention relates to a portable well diameter graduator for a multi-arm sidewall contact device, in particular to a portable well diameter graduator for a sidewall contact device; the sidewall contact device has a tubular basal body (11), and multiple backup arms (13) capable of being opened and retracted relative to the tubular basal body (11) and uniformly distributed in the peripheral direction of the tubular basal body (11); and the well diameter graduator comprises a scale plate (23), and single-lug and double-lug centering fixed bases (22, 27) respectively provided with holding parts (38, 48). The single-lug centering fixed base (22) and the double-lug centering fixed base (27) are fastened through a fastening device, so that the well diameter graduator can encircle the basal body (11), and the axes of the two can be overlapped. The scale plate (23) can be kept in the holding parts (38, 48), and can be pivoted relative to the latter to form a limiting position for limiting the opening degree of the backup arms (13); and the limiting position is corresponding to the calibration value for calculating the well diameter.