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gEDA-user: Verifying footprints



I realize this should be simple but I'm following the gEDA how to create footprints document and trying to understand how the numbers derived for specific footprints.  For example:  the pad definitions in the 0805.fp is as follows:

Pad[-3543 -393
-3543 393
5118 2000 5718 "1" "1" "square"]
Pad[3543 -393
3543 393
5118 2000 5718 "2" "2" "square"]

Excuse the crude sketch.
According to the gEDA how to create footprints document the dimensions for the 0805 are (these values are taken from the IPC-SM-782A Standard):

  C      X      Y       Z        G         Grid
74.8   59.1  51.2  126.0  23.6  157.5 x 315.0

So from the document the pad sizes as follows:

             |<-------- C -------->|
-------------------------------------------
|                                                    |
|     -----------              -----------     | ----------
|     |             |             |             |     |     
|     |      |      |             |      |      |     |      
|     |      |      |             |      |      |     |       X
|     |      |      |             |      |      |     |
|     |_______|              |_______|     | _______
|     |<- Y -->|<-- G -->|                   |
|_____________________________|
|<---------------- Z ------------------>|

Calculated dimensions:
C = 3543 * 2 = 7086 = 70.86 mils
X = 5118 = 51.18 mils
Y = 393 * 2 + thickness = 5904 = 59.04 mils
G = C - thicknes = 7086 - 5118 = 1968 = 19.68 mils
Z = C + thickness + clearance = 7086 + 5118 + 2000 = 14204 = 142.04 mils

If I calculated these values correctly, why are they off from the values in the IPC-SM-782A standard?
If I didn't calculate them correctly, where did I go wrong?
Is this a standard clearance?



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