Weighted pressures plates output different redstone signal strengths proportional to the number of entities sitting on them. However, if several entities land on them at the same time, they output signal strength 1 for a brief time before outputting a proportional signal strength. This limits their use. For example, they cannot detect the number of item entities passing over them in water streams.

Steps to reproduce

1. Place a gold (light) pressure plate on the ground and a long redstone line coming from it. (To see the redstone power level more clearly, place the redstone dust on solid blocks and place redstone lamps next to the solid blocks).
2. Above the pressure plate, place a block.
3. Drop several unstackable items on the block.
4. Break the block and watch the redstone output.
5. Make a 1-block wide water stream on ice.
6. Place a gold (light) pressure plate at the end of the stream, and make sure there is another block of ice after the pressure plate so that items can slide over it and past without getting stuck.
7. Block the water stream upstream of the pressure plate.
8. Throw several unstackable items into the water stream so that they push against the spot where it is blocked.
9. Break the blockage so that the items can flow down the stream.
10. Repeat all of the above with an iron (heavy) pressure plate and > 20 unstackable items in each case.

Expected results

The weighted pressure plates output a signal strength porportional to the number entities on them at all times.

Observed results

In step (4) the weighted pressure plates output a signal strength of 1 for about 1/2 second before outputting a signal strength proportional to the number of entities on them. In step (9) the weighted pressure plates only output a signal strength of 1 regardless of how many entites pass over them at one time because they do not update fast enough.