Inductive Formulas

This program calculates seven inductive formulas useful in electronics design, covering instantaneous voltage, single-layer coil inductance, L/R time constants, series and parallel inductors, coil Q factor, inductive reactance (XL), and the impedance of inductive/resistive circuits. Menu selection is stored in variable F but the branch logic erroneously tests variable U (which is never assigned), meaning formula dispatch never works as intended. A custom iterative square-root subroutine at line 3030 uses Newton’s method, converging by checking when successive corrections W equal zero or repeat, since the platform lacks a built-in SQR function. Unit conversions between millihenries and henries (dividing by 1E3) and microfarads and farads (dividing by 1E6) are handled inline throughout the calculation routines.

Program Structure

The program presents a numbered menu (lines 10–90) for seven inductive formulas, accepts a selection via INPUT at line 100, and then is supposed to branch to the appropriate calculation routine. The calculation blocks are spread across lines 120–590, followed by a standalone square-root subroutine at lines 3010–3090. Line 9992 provides a SAVE with auto-run, and line 9999 loops back to line 80 (the last menu item print) via GO TO VAL "80".

Critical Bug: Variable Mismatch in Dispatch

The user’s menu choice is read into variable F at line 100, but the branch conditions at lines 120–150 all test variable U, which is never assigned anywhere in the program. As a result, U will always be zero, none of the IF U=... branches will trigger, and execution falls through unconditionally to line 170 — the resonant frequency calculation block — regardless of which formula the user selects. All seven formula paths are effectively unreachable except that one. The correct variable in each condition should be F.

Incomplete Dispatch Table

Even if the variable were corrected, the dispatch logic is incomplete. The menu advertises seven formulas (#1 through #7), but the branch table only covers cases 3, 4, 5, and 6 (lines 120–150). There are no branches for selections 1, 2, or 7, and line 110 carries only a REM comment reading “LEFT OFF HERE,” suggesting the program was never finished. The blocks starting at lines 520–590 (labeled in the code for formula #7, impedance) are present but unreachable via any corrected dispatch.

Square-Root Subroutine

Because the platform lacks a native SQR function, a Newton’s-method iterative square-root routine occupies lines 3010–3090. It takes input in X and returns the result in Y, using W and Z as internal working variables.

1. Line 3030 short-circuits for X=0, returning Y=0 immediately.
2. Line 3040–3050 guards against negative inputs, printing an error and halting.
3. Line 3060 seeds the initial estimate as Y = X * 0.5.
4. Line 3070 computes the Newton correction: W = (X/Y - Y) * 0.5.
5. Line 3080 terminates when W=0 (converged) or W=Z (oscillating between two values), then returns.
6. Line 3090 updates Y and saves the previous correction in Z before looping.

Note that line 3030 uses the literal character O (letter O) rather than the digit 0 for the zero comparisons and assignment. On this platform, an uninitialized string variable named O would cause an error, but if O is treated as a numeric variable it defaults to zero — so the routine works accidentally but is technically a coding error.

Unit Handling

All electrical unit conversions are performed inline. Inductance values entered in millihenries are converted to henries by dividing by 1E3, and capacitance values in microfarads are converted to farads by dividing by 1E6. Results are scaled back to display units before printing (e.g., L*1E3, C*1E6).

Notable Idioms and Observations

• GO TO VAL "80" at line 9999 is a memory-saving idiom substituting a string literal for a numeric constant in the branch target.
• The resonant frequency formula at line 230 uses the constant 159 (approximation of 1/(2π) × 1000, accounting for the mH/µF unit scaling) rather than computing 1/(2*PI*SQR(LC)) explicitly, leveraging the custom subroutine output Y.
• Lines 235, 275, 315, 350, 430, 470, 510, 590, 3000, and 9989 all use STOP to terminate execution after each formula, preventing fall-through between blocks.
• The Q-of-circuit section (lines 360–510) uses INPUT with a prompt asking the user to type Q, F, or B as a letter, then compares the input to the BASIC variables Q, F, and B — a creative but fragile technique that depends on those variables being zero (their default) so the comparison resolves correctly only when the user enters 0.