4.3.3 Ring finger 5/16" rule
4.3.3 measurement
The ring finger span is often derived from the middle finger span rather than measured independently, using the 5/16" Ring Finger Rule. Spectre Cloud can apply this calculation for you through Auto-Calculate Ring Span (2.6.8), or you can enter the ring finger span manually.
📐 The Rule
The ring finger span is calculated as:
Ring Finger Span = Middle Finger Span + (5/16" − d)
Where d is the observed difference between the second joint lines of the middle and ring fingers, measured with the bowler's hand flat on the ball. When the joint lines are level (d = 0"), the ring span comes out 5/16" longer than the middle span; as d increases, the ring span shortens relative to the middle.
| d value | Adjustment (5/16" − d) | Effect on ring span |
|---|---|---|
0" | +5/16" | Ring span 5/16" longer than middle |
5/16" | 0" | Ring span equals middle span |
> 5/16" | Negative | Ring span shorter than middle |
⚙️ Auto Calculation in Spectre Cloud
When Auto-Calculate Ring Span is used:
- Enter the middle finger span as measured.
- Enter the d measurement in its field.
- Spectre Cloud calculates and displays the ring finger span using
Middle Span + (5/16" − d). - Review the result before saving.
⚠️ Verify with your Spectre team: confirm the exact field label for the d input and whether the calculated ring span is read-only or an editable value the operator can still override.
✏️ Manual Entry
If you measure the ring finger span directly, you can enter it manually instead of using the calculation — appropriate when you have independent measurements of both fingers, or when transferring an explicit ring span from a legacy sheet.
Related Sections
- 4.3.1 — Entering span measurements
- 4.4.5 — Inputting pitches
- 2.6.8 — Auto-Calculate Ring Span (the 5/16" rule)
- 05 — Oval Calculator
Tip: The 5/16" rule produces a starting span, not a fixed prescription. If a bowler reports the ring finger feels consistently tighter or looser than the middle despite a correct-looking sheet, re-check the d measurement first — it takes under a minute and often explains the complaint.