What is a signpost, conjunction or connective?

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Signpost words, often in the form of connectives or conjunctions, show the relationships between phrases and sentences. Pure connectives such as and or but should not be used at the start of sentences in formal academic writing; however, those that give information about how ideas relate or place them in a hierarchical relationship are helpful and placing them first allows the reader to see that the sequencing is critical to understanding the ideas being expressed: Subsequently, the chemicals were inserted in the bath.
The adverbial signpost is critical to show the order of the experiment: However, the chemical reaction was inconclusive.
Tells the reader that although procedure was followed, the result was not as expected. So the information given previously has faults:
Thus the heat exchanger generated excessive heat.
Tells the reader the outcome of the experiment and that this is a critical piece of information:
The chemicals were inserted into the bath and fully immersed for twenty seconds.
This simply gives the order of events. Splitting the sentence into two would make less sense as the actions occurred simultaneously, not in sequence.