Vendor/phpspreadsheet/phpoffice/phpspreadsheet/src/PhpSpreadsheet/Calculation/Financial.php
public static function TBILLEQ($settlement, $maturity, $discount)
    {
        $settlement = Functions::flattenSingleValue($settlement);
        $maturity = Functions::flattenSingleValue($maturity);
        $discount = Functions::flattenSingleValue($discount);

        //    Use TBILLPRICE for validation
        $testValue = self::TBILLPRICE($settlement, $maturity, $discount);
        if (is_string($testValue)) {
            return $testValue;
        }

        if (is_string($maturity = DateTime::getDateValue($maturity))) {
            return Functions::VALUE();
        }

        if (Functions::getCompatibilityMode() == Functions::COMPATIBILITY_OPENOFFICE) {
            ++$maturity;
            $daysBetweenSettlementAndMaturity = DateTime::YEARFRAC($settlement, $maturity) * 360;
        } else {
            $daysBetweenSettlementAndMaturity = (DateTime::getDateValue($maturity) - DateTime::getDateValue($settlement));
        }

        return (365 * $discount) / (360 - $discount * $daysBetweenSettlementAndMaturity);
    }
public static function TBILLEQ($settlement, $maturity, $discount)
    {
        $settlement = Functions::flattenSingleValue($settlement);
        $maturity = Functions::flattenSingleValue($maturity);
        $discount = Functions::flattenSingleValue($discount);

        //    Use TBILLPRICE for validation
        $testValue = self::TBILLPRICE($settlement, $maturity, $discount);
        if (is_string($testValue)) {
            return $testValue;
        }

        if (is_string($maturity = DateTime::getDateValue($maturity))) {
            return Functions::VALUE();
        }

        if (Functions::getCompatibilityMode() == Functions::COMPATIBILITY_OPENOFFICE) {
            ++$maturity;
            $daysBetweenSettlementAndMaturity = DateTime::YEARFRAC($settlement, $maturity) * 360;
        } else {
            $daysBetweenSettlementAndMaturity = (DateTime::getDateValue($maturity) - DateTime::getDateValue($settlement));
        }

        return (365 * $discount) / (360 - $discount * $daysBetweenSettlementAndMaturity);
    }
TBILLEQ.

Returns the bond-equivalent yield for a Treasury bill.

@param mixed $settlement The Treasury bill's settlement date.
The Treasury bill's settlement date is the date after the issue date when the Treasury bill is traded to the buyer.
@param mixed $maturity The Treasury bill's maturity date.
The maturity date is the date when the Treasury bill expires.
@param int $discount The Treasury bill's discount rate

@return float