Sine deformer offset expression issue

Hi

I get reverse jump on the sine deformer when i set an expression on the " offset "

When i set the attribute to 10 for fast motion and then set attribute 2 for slow motion...it gives me reverse effect...

The expression has the speed attribute on the placer control...

The expression is as below:

sine1.offset = (time*placer.speed)*-0.1;

Can anyone help me on this...i cannot change the rig as it is control by sine deformer...

It would be greate if i get the proper expression code for sine offset only...