The term “one/one” refers to the delivery of one movement/instruction at a time so that students can perform the instruction as it is delivered.
This is a skill required where students need time to orientate themselves. For example, in bharadvajasana I, students are often confused by which side, which hand etc. It is more effective if instruction is delivered in small packets of information.
One/one does not require a demonstration and the asana can be performed with the students so that the visual is current as they apply the instruction. This exercise trains us to refine the delivery of information and to economise on language. This exercise works well for large groups of students and provides an effective means of managing time. As you deliver the information in packets (short statements) that can be applied, observe the performance before providing the next instruction.