# SDRAM timing confusion

I'm looking at this data sheet: T67M-512Mb-Mobile-Lpddr-Sdram (targeting speed grade -75) and trying to understand the timing requirements for performing a read, specifically when to sample the DQ input data lines. It gives a formula on page 27 for Data valid output window (DVW) being tQH - tDQSQ

Writing down the min and max values as <min,max> in unit of nanoseconds, I find tDQSQ on page 26 as <-,0.6> . I assume if the minimum is not stated, the worst case is 0?

A formula is given for tQH on page 27 as tHP-tQHS. tQHS is on page 27 and given as <-,0.75> while yet another formula is given for tHP as tCH,tCL. Not sure what a comma means here.

tCH and tCL are both found on page 26 with values of <0.45,0.55>

Plugging in all my values, I get a final formula of:

(<0.45, 0.55> - <0.0, 0.75>) - <0.0, 0.6>

This formula confuses me as there are values within the ranges that can result in an overall valid window time of zero, or even a negative value.

Am I calculating/interpreting this correct? Do these values means that there are no gaurantees that the output data will be valid?