0.129 nm although you often see it at 0.13 nm

Two half arrows are usually used to denote a reaction which is in equilibrium. If they are the same length to one another then equilibrium is obtained and you have a mixture of reagent and product.

If the arrow pointing right is larger then this denotes that the reaction is predominently a forwards reaction and favours the product and vice versa.

The length of the pendulum is measured from the pendulum's point of suspension to the center of mass of its bob. Its amplitude is the string's angular displacement from its vertical or its equilibrium position.

equilibrium conversion is that which is at equilibrium concentration

above equilibrium