What are the reasons for rounding percentages between the percentages of time spent by one parent and the other parent?

Canada (Federal), Canada

The following excerpt is from Morrissey v. Canada, 2019 FCA 56 (CanLII):

In so concluding I adopt and make mine the Reasons of my colleague Webb J.A. in Alexey Lavrinenko v. Her Majesty the Queen (2019 FCA 51) (A-410-17) [Lavrinenko] which I have had the occasion of reading in draft and with which I am in entire agreement. More particularly, I agree entirely with paragraphs 37 and 41-42 of Webb J.A.’s reasons wherein he states that “near equal” means “almost equal” and hence that “any percentage of time that cannot be rounded off to 50% would not qualify as near equal” (para. 41). As Webb J.A. explains, at paragraph 42 of his reasons, any rounding of percentages should be to the nearest whole number that is a multiple of 10 and another whole number. Specifically, any percentage between 45% and 49% should be rounded upwards to 50%, while any percentage between 41% and 44% should be rounded downwards to 40%. This approach addresses the concern that, due to a lack of precise data, “it is not always possible to accurately quantify the number of hours that the child resides with each parent and, therefore, arrive at a precise determination of the percentage of time that the child resides with each parent” (para. 42).

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