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I looked at the dimensions drawing of the SOIC‑14 package from texas instruments. But I am a bit confused about the way texas instruments marked some lengths. Why there are two values seperated by a horizontal line for one length? Which one is the correct?

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    \$\begingroup\$ minimum and maximum size. Everything has a tolerance. \$\endgroup\$ – markrages May 2 '16 at 13:58
  • \$\begingroup\$ a thought: I'm in the habit of placing parts on printouts of my pcb before production. rounding errors have caused alignment errors on large packages. squeezing pins onto pads is time consuming and terrible \$\endgroup\$ – b degnan May 2 '16 at 15:47
  • \$\begingroup\$ @bdegnan The most important thing is the pin spacing and it's a "Basic" (theoretically exact) dimension (indicated by the box around it). \$\endgroup\$ – Spehro Pefhany May 2 '16 at 15:51
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These are minimum and maximum size (in both inches and mm). As you see the difference is very small. Simply make sure that everything still works as intended with both sizes; regarding footprints that means making the pads slightly larger than the maximum size. In case you solder by hand make them about 1mm longer than the leads too.

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