Systems and methods for determining rheology characteristics of a drilling fluid include a drop-in unit sized to fit within a flowline of a drilling fluid circulation system upstream of a mud shaker. The drop-in unit has an entry funnel having an end plate with an opening through the end plate. The entrance of the entry funnel has an outer diameter that is larger than a diameter of the opening through the end plate. An instrumentation tubular is an elongated member with an inner bore that is in fluid communication with the opening through the end plate. The instrumentation tubular includes a downstream sensor and an upstream sensor. The upstream and downstream sensors are operable to sense a parameter of the drilling fluid traveling through the instrumentation tubular for calculating a change of viscosity of the drilling fluid within the flowline between a first time and a second time.