A rotor of a fluid machine comprising: a wheel that is supported for rotation about an axis of rotation , the wheel having a hub and a back disc extending radially away from the hub and terminating in a radial direction at an outer rim edge , the back disc having a front face and a back face ; a plurality of blades included on the wheel, the plurality of blades projecting from the front face of the back disc ; an inter-blade area defined circumferentially between a first blade and a second blade of the plurality of blades with respect to the axis of rotation, wherein the first blade includes a pressure side , and the second blade includes a suction side , the pressure side facing toward the suction side across the inter-blade area, and wherein the wheel includes a first fillet at a transition between the inter-blade area and the first blade and the wheel includes a second fillet at another transition between the inter-blade area and the second blade; and a balancing mark on the wheel and within the inter-blade area, the balancing mark being elongate and having a first end and a second end , the first end and the second end being stepped axially into the inter-blade area, the balancing mark extending arcuately between the first end and the second end, the balancing mark having a depth that varies as the balancing mark extends arcuately between the first end and the second end, the balancing mark having a width that varies as the balancing mark extends arcuately between the first end and the second end, wherein the first end is disposed proximate the pressure side of the first blade, and wherein the second end is disposed proximate the suction side of the second blade, wherein the first end is deeper than the second end; and wherein the first end is recessed into the first fillet and the second fillet is uninterrupted by the second end. a wheel that is supported for rotation about an axis of rotation , the wheel having a hub and a back disc extending radially away from the hub and terminating in a radial direction at an outer rim edge , the back disc having a front face and a back face ; a plurality of blades included on the wheel, the plurality of blades projecting from the front face of the back disc ; an inter-blade area defined circumferentially between a first blade and a second blade of the plurality of blades with respect to the axis of rotation, wherein the first blade includes a pressure side , and the second blade includes a suction side , the pressure side facing toward the suction side across the inter-blade area, and wherein the wheel includes a first fillet at a transition between the inter-blade area and the first blade and the wheel includes a second fillet at another transition between the inter-blade area and the second blade; and a balancing mark on the wheel and within the inter-blade area, the balancing mark being elongate and having a first end and a second end , the first end and the second end being stepped axially into the inter-blade area, the balancing mark extending arcuately between the first end and the second end, the balancing mark having a depth that varies as the balancing mark extends arcuately between the first end and the second end, the balancing mark having a width that varies as the balancing mark extends arcuately between the first end and the second end, wherein the first end is disposed proximate the pressure side of the first blade, and wherein the second end is disposed proximate the suction side of the second blade, wherein the first end is deeper than the second end; and wherein the first end is recessed into the first fillet and the second fillet is uninterrupted by the second end. <EOS>