Unit's heavy machinery initially located below Bakerloo's terminus (3)
I believe the answer is:
ohm
'unit's' is the definition.
(ohm is a kind of unit)
'heavy machinery initially located below bakerloo's terminus' is the wordplay.
'initially' says to take the initial letters.
'located below' is a charade indicator (letters next to each other).
'bakerloo's terminus' becomes 'o' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
The initial letters of 'heavy machinery' is 'hm'.
'hm' after 'o' is 'OHM'.
Can you help me to learn more?
(Other definitions for ohm that I've seen before include "measure of resistance" , "Unit of electrical resistance (3)" , "physical unit" , "SI unit of electrical resistance" , "Physicist" .)