Inverse sliders, vlookup and cell referencing

Hi - any assistance greatly appreciated. Please see file attached.

I have two sliders operating so that changing the value of one slider inversely changes the value of the other.
I have done this by creating a vlookup function that picks out the inverse value I require from the appropriate table and then I make the slider linked cell equal the vlookup cell and Bob's your uncle - and in fact, he is my uncle!! ....anyway

If I then use one of the sliders I can move it left and right quite happily and the other slider moves inversely. Great.

The problem occurs when having used one slider, I try and move the other slider. Both the linked cell references to the vlookup cells break and the sliders cease to work in tandem.

I cannot seem to get the cell reference from the linked cell to permanently look at the value created in the vlookup cell.

I have tried everything I can think of without success. If anyone can help before I lose what's left of my hair I'd be very grateful.

Thanks.