I can't get the dimensions of my model parts to be stable

For example, using the push/pull too, I type in a number for the dimension I want and I then click on return or click on the mouse, but it often stretches the model to some other dimension. Using Safari with a Catalina version operating system.

Are you clicking in the Measurements window before typing the dimension? If so, don’t. Start the push/pull operation and then let go of the mouse and type the distance.

Be sure to press the Return or Enter key to complete the numeric entry of the dimension. I’m just stating this for completeness, based on the original post’s comment “…or click on the mouse” after typing in a number (which makes me wonder if @tingaling is typing in some digits and then clicking the mouse somewhere without pressing Return).