Measurement of distance covered by assembling Tory demo (8)

I believe the answer is:

odometry

'measurement of distance covered' is the definition.
(odometry means the measure of distance travelled)

'assembling tory demo' is the wordplay.
'assembling' indicates anagramming the letters.
'tory'+'demo'='torydemo'
'torydemo' is an anagram of 'ODOMETRY'.

'by' acts as a link.

(Another definition for odometry that I've seen is " Method of estimating distance travelled".)

I've seen this clue in The Independent.

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