I'll give you one more clue for this puzzle: the sum of numbers from 1 to 6 is 21. In column 4, you have two cages with clues "8+" and "12+". Well, those two add up to 20. Now, since we know that in this column, column 4, as in any other column, all numbers must add up to 21, it means that the remaining cell in this column MUST BE 21-20=1. Therefore, R1C4 (row 1, column 4) = 1, which immediately also solves it's "buddy" cell (the cell in the same cage) - R1C5 = 5. (Why?) This technique is called "innies/outies" and it's use is not as common in CalcuDoku puzzles as it is in Killer Sudoku.
Oh, by the way, if the operator next to a number is missing, it's not a mistake. You have to figure out what it must be! In this particular puzzle, it's quite easy to do that, unlike in some more difficult ones.
As you can see, unlike Sudoku, there is some math involved. Don't be put off by this. These puzzles are very addicting but arguably even more satisfying when finished and in fact, they are being used for educational purposes in schools.
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