At frequencies away from the resonant frequency, the impedance includes some reactance (capacitance or inductance). As frequency increases, inductive reactance also increases and capacitive reactance decreases. The larger the SCR, the smaller is alternator reactance (Xd) and inductance Ld. Both inductive and capacitive loads create what is known as reactance in an AC circuit. Impedance is a combination of two quantities&colon; resistance and reactance. The sum of oppositions to current flow from both resistance and reactance is called impedance. The ratio of peak voltage to peak current is due to capacitive reactance (denoted X). Negative capacitances and inductances are "non-Foster" circuits which violate Foster's reactance theorem. In 1986, Lukaski published empirical equations using the impedance index, body weight, and reactance. Capacitive reactance is "X" = . These formulas are valid for an ideal resistor, with zero reactance. There are two choices in the literature for defining reactance for a capacitor. The unit of reactance is the ohm. These reduce the reactance of the armature, and improve the commutation. NIC circuits were used to cancel reactance on telephone cables.