Digital Twin (DT) refers to the virtual copy or model of any physical entity (physical twin) both of which are interconnected via exchange of data in real time. Conceptually, a DT mimics the state of its physical twin in real time and vice versa. Application of DT includes real-time monitoring, designing/planning, optimization, maintenance, remote access, etc. Its implementation is expected to grow exponentially in the coming decades. The advent of Industry 4.0 has brought complex industrial systems that are more autonomous, smart, and highly interconnected. These systems generate considerable amounts of data useful for several applications such as improving performance, predictive maintenance, training, etc. A sudden influx in the number of publications related to ‘Digital Twin’ has led to confusion between different terminologies related to the digitalization of industries. Another problem that has arisen due to the growing popularity of DT is a lack of consensus on the description of DT as well as so many different types of DT, which adds to the confusion. This paper intends to consolidate the different types of DT and different definitions of DT throughout the literature for easy identification of DT from the rest of the complimentary terms such as ‘product avatar’, ‘digital thread’, ‘digital model’, and ‘digital shadow’. The paper looks at the concept of DT since its inception to its predicted future to realize the value it can bring to certain sectors. Understanding the characteristics and types of DT while weighing its pros and cons is essential for any researcher, business, or sector before investing in the technology.

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in the normal subject, to be about 0 4 ms from conduction in the roots'0 and therefore correction of normative data is necessary where there is slowing of peripheral motor conduction. Proximal root conduction time was calculated as 10 ms for motor conduction velocity (neck-wrist) of 30 ms -' and 1 5 ms for 20 ms' -giving upper limits of CMCT of8-9 ms and 9 4 ms respectively.

The clinical and electrophysiological findings in 22 patients with chronic trigeminal sensory neuropathy are described. The main clinical feature was slowly evolving unilateral or bilateral facial numbness sometimes associated with pain and paraesthesiae and commonly with disturbed taste. Nine patients had either systemic sclerosis or mixed connective tissue disease. Of the 13 other patients, 9 had either organ or nonorgan specific serum autoantibodies. Blink reflex latencies were recorded in 17 patients, the commonest abnormality being an 'afferent' defect with modest prolongation of latency. Trigeminal sensory evoked responses were recorded in 14 cases, 6 showing mild prolongation of latencies. It is suggested that the lesion in this type of trigeminal neuropathy is in the trigeminal ganglion or in the proximal part of the main trigeminal divisions. This conclusion is supported by limited pathological data.