Improvement of the "Zoom lock" algorithm in case when initial zoom <>100

Hi

There are couple examples of "Zoom lock" algorithm:

- Level/Zoom = 10/100%

- "zoom lock" on: 10/200%

- "zoom lock" off: 10/100%

it's ok,

Now i manually set zoom<>100%, for example = 40

- Level/Zoom = 10/40%

- "zoom lock" on: 10/200%

- "zoom lock" off: 10/100%

but i think would be more logical to have:

- Level/Zoom = 10/40%

- "zoom lock" on: 10/80%, i.e. 40%*2

- "zoom lock" off: 10/40%, i.e. return to exactly the same level and zoom as were before "zoom lock" mode