qc is cone resistance measured with the Cone Penetration Test (CPT) where a cone is pushed into the ground at a constant speed (e.g. 2cm/second). It’s also know as the static cone penetration test. qd is cone resistance but measured dynamically and is known as the Dynamic Cone Penetrometer (DCP). To do a comparative test, the geology should be the same so test probes should be done approx 30-40cm apart. A minimum of three comparative tests would be required. When comparing qc and qd, care needs to be taken with sandy soils because of lateral friction / skin friction on the rods.