Remember whenever you evaluate a term that is within a function such as ln, exp, sin, etc, the term should be dimensionless. If it is not, then keep checking until you find either an error in your work or an error in the printed equation that you are working from.

Also remember to check the units you calculate to be sure they are what you expect. If they are not coming out as you expect evaluate both your work and the form of the expression.

It is not unusual for equations to be published with errors. Sometimes it is not clear if a group of variables is in a denominator or just the first value is in the denominator. For example, t/dk is not clearly t/(dk) or (tk)/d, but if the term is in a function such as ln(t/dk) and the variables have the following units: t:T d:L and k:LT^-1, then you know it must be (tk)/d so that the units are TLT^-1L^-1 and the term is dimensionless.

On the other hand, if this term was not within a function and you expected a result with the units T²/L², then you would interpret it as t/(dk) because that would yield units of TL^-1L^-1T or T²L^-2 or T²/L².