I see these frequently on PCB figures (REF BSC TYP). Could someone
kindly explain what these mean? REF = reference (to what)? I pretty
sure that BSC is basic spacing between centers? TYP = ?


Also, in datasheet packaging sections, there is often a thin
horizontal rectangle subdivided into (usually) 3 or 4 sections. Each
rectangle usually starts w/ a symbol (for example, 1/2 circle or
theta)in the first section, followed by sections w/ alphas or
numberics - oftentimes accompanied by a letter in a circle. Could
someone explain this or point me to an explanation as well?

Thanks, Tom

Blip,

BSC: Basic Dimension. Theoretically exact value shown without tolerances.

REF: Reference Dimension, usually without tolerance, for information purposes only.

TYP: "typical" dimension.

The details you seek are all dimensioning standards encompassed in ANSI Y14.5M, search the internet for it and you will find your answers. However I am not sure you will find an online source, a quick search I did only turned up books for sale, no online versions.

The rectangular boxes with symbols and figures is part of the ANSI standard dimensioning where the figures indicate the type of measure/tolerance (center point, perpendicular, surface flatness, parallelism, etc., etc.), the letter usually indicates a datum to which the measure/tolerance pertains and the numerics are typically the actual measure and/or tolerance.