I am encounter another minor problem, cant figure out why the calculated cannot be shown two times in the calculation sheet



See attached calculation
WT Calculation.sm (62.69 KiB) downloaded 1099 time(s).

Use the function eval
WT Calculation1.sm (63.7 KiB) downloaded 1083 time(s).

Is this a common / default practise to follow each time using Findroots? why is other formula dont required the function eva? I am starting to get very confuse

BTW, ... either <, > rarely exist in maths.
Define completely as shown.

Maybe there is a bug.
Is this same with everyone?

findroot_bug.sm (18.75 KiB) downloaded 1014 time(s).

The problem is due to the embedded assignment in FindRoot.

When t_thick is defined, the solution command is just stored but not executed.

It is first time executed, when t_thick is displayed. At that point, t.t gets defined by internal assignment.
At the second attempt to display t.thick, this fails because FindRoot needs undefined variables.

using eval() enforces immediate execution of FindRoot and assigns the result to t.thick.

Subsequent references to t.thick just display the stored value instead of executing FindRoot again.

Thank you to all your guidance and advice. Learned another trick today.!!