In the field of 5 to 100 kg load transportation in workshops, many systems having more or less complex architectures have been developed to reduce musculo-skeletal disorders (hoists, pliers, dedicated systems). These systems offer different behaviors and human interaction is far from being the same for all of them. In recent years, the literature has produced a lot of work around design thinking, user-centered approaches emphasizing notions around perception, cognition, and ergonomics to meet the needs of the end user. The development of cobotics and more generally systems allowing the interaction or co-manipulation of objects highlights the notion of transparency of the system. This transparency is expressed as the fact of feeling only a part of the physical magnitudes of the object most relevant to the user in his manipulation. In the context of this article, we study the transparency of a kinematically redundant passive mechanism when manipulating heavy objects on a plane. This article is based on a state of the art of different criteria in order to evaluate the behavior of a robot such as manipulability or dexterity. We will indicate the relevance of these criteria that we apply to a theoretical study. These theoretical aspects will then be evaluated on Neoditech Scara Parts arm. It is a mechanism capable of handling up to 50kg composed of a plane arm mounted on vertical linear axis itself mounted on a fixed or mobile base. This plane arm consists of 6 rotational joints having parallel axes ensuring redundancy in the architecture of the robot. It is known for its fluidity and transparency to its users. This article focuses on finding the causes of this reputation and evaluating them.