PGCE Comments

• Explain what is meant by `physical quantity'. -- clark: In the Introduction section, I replaced 'physical quantity' with 'measurement of a physical phenomenon'. Don't know if that's much clearer, really.
• Chapter is too full of tables and words need figures to make it more interesting.
• Make researching history of SI units a small project.
• Multiply by one technique: not positive! Suggest using exponents instead (i.e. use the table of prefixes). This also works better for changing complicated units (km·h⁻¹ to m·s⁻¹ etc....). Opinion that this technique is limited in its application.
• Edit NASA story.
• The Temperature section should be cut-down. SW: I have edited the original section but perhaps a more aggressive edit is justified with the details deferred until the section on gases.