I could be wrong but I'd say that solution will only provide one value, not a range.
maybe
=IIf([TEST1_Compaction]<=[Project_Spec]+[Spec_Allowence_Compaction] AND [TEST1_Compaction]>=[Project_Spec]-[Spec_Allowence_Compaction],"Pass","Fail") ?
Hard for me to say because I see no form field called Project_Spec but if I use Compaction_Spec I get a range of 95.2 to 100.8 which is a fail in this case.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.