with reference to fig1 and 2 , the measuring rod 10 according to an embodiment of the invention has a section of epicycloidal shape . the section is illustrated more particularly in fig1 . the outer epicycloidal profile 11 of the measuring rod 10 according to an embodiment of the invention is constructed from three isometric arcs ( or curved portions epicycloid ) referenced a 1 , a 2 , a 3 each being constructed from circle of the same radius . the inner epicycloidal profile 13 of the measuring rod 10 is constructed from three isometric arcs a 1 ′, a 2 ′, a 3 ′ respectively concentric to the isometric arcs a 1 , a 2 , a 3 forming the outer profile 11 . the work centers c 1 , c 2 , c 3 of the isometric arcs a 1 , a 1 ′, a 2 , a 2 ′, a 3 and a 3 ′ are represented schematically by a point in fig1 . in this manner , the measuring rod 10 has an inner space 12 suited to the passage of instrumentation strands . the section of epicycloidal shape of the rod according to an embodiment of the invention is particularly beneficial because it makes it possible , at iso - mass , to obtain a gain of the order of 10 % in frequency in the dynamic behavior of the measuring rod compared to a rod of the prior art having a circular section . in addition , such an epicycloidal profile has a dynamic resistance greater than measuring rods having a circular profile with grooves positioned radially to the periphery of the rod . the profile according to an embodiment of the invention makes it possible to meet the geometric size requirements of turbomachines in which the measuring rods are positioned . thus , the profile of the rod according to an embodiment of the invention makes it possible to guarantee a satisfactory passage section between the ventilation rod and the measuring rod so as not to perturb the characteristics of the ventilation circuit that passes between the two rods . in comparison with a measuring rod with circular profile , the measuring rod according to an embodiment of the invention has an outer size reduction of 25 % at iso - mass . the inner space 12 makes it possible to ensure the routing of instrumentation strands . in comparison to measuring rods of circular profile , the internal space 12 of epicycloidal shape has an enlargement of the inner section of the order of 20 %. the measuring rod according to an embodiment of the invention can easily be manufactured by a laser fusion method . thus , the solution presented proposes a not very cumbersome system for the passage of cables which enables a greater assembly of instrumentation compared to existing solutions .