1) Imperceptible 2) Insignificant 3) Unimportant 
• (a.) Not appreciable; too small to be perceived; incapable of being duly valued or estimated.
In`ap·pre'ci·a·ble adjective [ Prefix in- not + appreciable : confer French inappréciable .] Not appreciable; too small to be perceived; incapable of being duly valued or estimated. Hallam. 
[adj] - too small to make a significant difference
adjective too small to make a significant difference; `inappreciable fluctuations in temperature`
imperceptible; insignificant: an inappreciable difference.