What is in the chart

Butt-weld tab. 90 LR (1.5 × the pipe size), 90 SR (1 × the size, from 1 inch up, since short radius is not made smaller), and 45 LR, using the commonly published center-to-end dimensions.
Threaded and Socket-weld tabs. Empty on purpose: "Type the take-out from your fitting maker's chart. Nothing ships for these." Make-up varies too much by maker to guess.
Every value is labeled "Default values. Check your fittings." Any value you edit can be put back with "Reset to default".

How the offset tools use it

When you pick 2 inch and 45 LR in the simple offset tool, the 1 3/8 inch take-out comes from this chart. At angles other than 45, the tools use the 90 LR or 90 SR value cut down to the angle (center-to-end × tan of half the angle). Edit a value and every new offset uses your number. Cuts already saved keep the numbers they were made with.

Free and Pro

The 1/2, 3/4, and 1 inch rows are free to read. Sizes from 1 1/4 to 12 inch sit behind a panel titled "Every pipe size and fitting". Pro opens every row, lets you tap any value to edit it, and lets you type in threaded and socket-weld take-outs.

The default values themselves are not a secret: the whole chart, in fractions and decimals, is printed in the pipe take-out chart guide. What the app adds is that the chart is wired into the offset math, and holds your corrections.

The weld gap lives here too

A butt weld needs a root gap, so a two-elbow offset loses two gaps from the cut. FitUp uses 1/8 inch per joint by default for welded trades and none for plumbing. Threaded and socket-weld take-outs carry their own allowance, so no gap is added to them. Pro lets you set the gap per joint anywhere from 0 to 3/16 inch to match your procedure. Why both allowances matter is covered in how to figure take-outs and cut length.