The readings are imprecise because the needle wavers so much.
Advanced English Dictionary
+adjective not accurate; not giving exact details or making sth clear: an imprecise definition + imprecise information + The witness's descriptions were too imprecise to be of any real value. Antonym: PRECISE imprecisely adverb: These terms are often used imprecisely and interchangeably. imprecision noun [U]: There is considerable imprecision in the terminology used.
Collocation Dictionary adj
be, seem | become
extremely, very | fairly, rather, somewhat | notoriously
‘Breach of the peace’ is a notoriously imprecise notion.
She was rather imprecise about the cost of the trip.
Random quote: Impossibilities are merely things which we have not yet learned.: Charles Chesnutt