```ts
/**
 * The value added to a running total by one instruction.
 */
export function stepValue(step: string): number {
  if (step === "+") {
    return 1;
  }
  if (step === "-") {
    return -1;
  }
  return 0;
}

/** The running total after each instruction. */
export function scanTally(steps: string[]): number[] {
  let total = 0;
  const results: number[] = [];
  for (const step of steps) {
    total += stepValue(step);
    results.push(total);
  }
  return results;
}
```