Cheat Engine

[magellenproject]

Hello I am still fairly unsure of my way around CE It seems.

I have have these codes:

004F438c mov eax,edx // when I replace this with add eax,edx
I can get a very short lived boost of speed, but then my speed fluctuates between 220 and 117(default is 119), until i revert the code back to its previous state.
I cant go much over 280 or something like that, without it "jumping back"
Am I right in saying [esi+10] holds the value of my speed?

I dont know what I am doing I could really use your help.

004F438E mov [esi+10],eax //This might move the input accumulated value from pressing the speed up button into the speed button.
Is that right?
I am not sure.

004F4391 mov esi,[esi]
004F4393 cmp dword ptr [esi],00
^^I dont know what those do
Any ideas as to how I can make a speed hack with these codes??