Speed of a Sine

I have a sprite with a sine behavior; Period: 5, Magnitude: 100. How do I measure its speed?

The linear speed is variable, I guess you can calculate it by checking the position at several time intervals.

You initialize the oldXposition of the sprite.

Every S seconds you get the newXposition of the sprite, calculate the speed with ABS(newXposition-oldXposition) and just afterwards update the oldXposition with the newXposition value.

This will give you the speed in px per S seconds you have defined. If the S value is too small, reaching the per tick system limit, I guess that it will give bad readings. The speed of the sine goes from 0 in the edges to the max speed when passing the initial point.

Will this method give me an accurate number? It seems that sine behavior does not have one constant speed as it is always changing.

There has to be a way. Maybe there is a way to measure how many pixels it is moving every tick?

Change the every x seconds in the above answer to every tick and....