Definition:
Moving Average Convergence Divergence: juxtaposition of two exponential moving averages; the expanding or contracting space between two exponential moving averages.
The MACD is composed of two moving averages of an item. This distance between the two moving average provides an early hint as to direction or changes in direction. Since the moving averages are not actual prices, they are derivatives of price.
The histograms measure the distance between the two moving averages. As such histograms are actually derivatives of derivatives. At any rate, I find histograms very valuable. The weekly histograms supersede the daily histograms, but when the daily histograms continue in one direction, in due time, they will impact on the weekly histograms.