How many times do you have to use the two-pan balance?

Question

Suppose you have 8 watermelons that are exactly the same in appearance.
They are equal in weight except for one, which is heavier than the others.
You want to find the heaviest one by using a two-pan balance.
Each pan can hold any number of watermelons,
and the only items that you can place in the pans are watermelons.

Find the best strategy to determine the heaviest watermelon.
In the worst case scenario,
How many times do you have to use the two-pan balance ?

Answer 1

Twice

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Strategy 1.

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1) Make 2 groups of 4, measure, 2) make 2 groups of 2 from the heavier group, measure, 3) measure the heavier group 1+1 to identify the heaviest one.
4+4 ---> 2+2 ---> 1+1 , total 3 measurements
Strategy 2.

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1) Make 3 groups of 3/3/2, measure 3 and 3, If they are equal, 2.1) measure 1+1 and find heavy one, if one group of 3 is heavier on first measurement, then, 2.2) divide the heavier group into 3 and measure 1+1, if any one is heavier, it is found, if they are equal then the reminder in group is the heaviest one.
3+3+2 ---> 1+1, total 2 measurements

As you can see the best is the strategy 2.