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docs/rack-planner/cable-length.md

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+# Cable Length Calculation
+
+## Goal
+
+Estimate practical cable lengths from the physical arrangement of devices in a rack so users can preselect realistic patch and power cable variants.
+
+The result should support planning, not exact installation certification.
+
+## Use cases
+
+- patch cable length between patch panel and switch
+- DAC or fiber estimate between devices in the same rack
+- power cable estimate from PDU to active device
+- BOM generation for preconfigured cable sets
+
+## V1 approach
+
+Cable length should be estimated from:
+
+- rack unit position of both components
+- side of connection: front or rear
+- optional port offsets
+- route style
+- slack factor
+
+## Suggested routing model
+
+For V1, use a rule-based path estimate instead of full geometric routing.
+
+### Inputs
+
+- source component `U` position
+- target component `U` position
+- source and target side
+- rack depth
+- routing preference
+- slack percentage or fixed reserve
+
+### Routing preferences
+
+- `front_vertical`
+- `rear_vertical`
+- `front_to_rear`
+- `shortest_practical`
+
+## Example calculation logic
+
+Estimate length as:
+
+1. vertical distance between source and target mounting positions
+2. plus horizontal or side transition allowance
+3. plus front/rear traversal allowance
+4. plus slack reserve
+
+Illustrative formula:
+
+```text
+estimated_length =
+  vertical_distance_mm
+  + side_transition_mm
+  + front_rear_allowance_mm
+  + service_loop_mm
+```
+
+Then round up to the next marketable cable length, for example:
+
+- `0.25 m`
+- `0.5 m`
+- `1.0 m`
+- `1.5 m`
+- `2.0 m`
+- `3.0 m`
+
+## Accuracy strategy
+
+The tool should display:
+
+- raw estimated length
+- recommended order length
+- confidence note such as `estimate only`
+
+## Data requirements
+
+Better cable estimation becomes possible if components expose ports with offsets.
+
+Minimum V1:
+
+- component `U` position only
+
+Better V1:
+
+- per-port offsets in the component metadata
+
+## BOM integration
+
+Cable entries can be generated as:
+
+- one line per connection
+- or aggregated by cable type and recommended order length
+
+Example:
+
+- `12 x RJ45 patch cable Cat6A, 0.5 m`
+- `4 x C13 to C14 power cable, 1.5 m`
+
+## Future improvements
+
+- front and rear cable manager objects
+- reserved routing channels
+- left/right side path selection
+- bend radius constraints
+- color-coded cable groups
+- cross-rack cable planning