In Kubota Vernacular - Reference Value & Allowable Limit
For example on my M4500 valve stem to guide clearance reference value = 0.0016 to 0.0028. Allowable limit = 0.0039. So... new or rebuild shoot for somewhere inside the reference value range, when simply reassembling old or re-using you can use it as long as it's under the allowable limit (you'd probably normally call it the "service" limit).