Add size chart

README.md

@@ -21,16 +21,20 @@ Image source: https://www.gearbest.com/sleeping-aids/pp_3003173012343574.html
 
 Image source: https://www.3m.com/3M/en_US/company-us/all-3m-products/~/3M-Particulate-Filter-2097-07184-AAD-P100-with-Nuisance-Level-Organic-Vapor-Relief-100-EA-Case/?N=5002385+3294780246&rt=rud
 
+### Reasoning for N95 filters
+
+![Virus Size](static/CoronaVirusSize.pjg)
+
 ## Initial Prototypes
 
 ### Initial Bill Of Materials
 
-* 120 mm ID O-Ring [McMaster P/N 9262K881](https://www.mcmaster.com/9262k881)
-* M4 x 0.7 mm, 12 mm long [McMaster P/N 91294A192](https://www.mcmaster.com/91294a192)
-* M4 x 0.4 mm, Nylon Locknuts [McMaster P/N 90576A103](https://www.mcmaster.com/90576a103)
-* 3M P100 Filters, 4.3" OD [3M 2097](https://www.3m.com/3M/en_US/company-us/all-3m-products/~/3M-Particulate-Filter-2097-07184-AAD-P100-with-Nuisance-Level-Organic-Vapor-Relief-100-EA-Case/?N=5002385+3294780246&rt=rud)
+* 120 mm ID O-Ring (seal around filter for assembled upper & lower housing), [McMaster P/N 9262K881](https://www.mcmaster.com/9262k881)
+* M4 x 0.7 mm, 12 mm long Philips head screws, [McMaster P/N 91294A192](https://www.mcmaster.com/91294a192)
+* M4 x 0.4 mm, Nylon Locknuts, [McMaster P/N 90576A103](https://www.mcmaster.com/90576a103)
+* 3M P100 Filters, 4.3" OD, [3M 2097](https://www.3m.com/3M/en_US/company-us/all-3m-products/~/3M-Particulate-Filter-2097-07184-AAD-P100-with-Nuisance-Level-Organic-Vapor-Relief-100-EA-Case/?N=5002385+3294780246&rt=rud)
 * Upper & Lower 3D printed housing (TBD)
-* XTC 3D Resin Coating for 3D prints (sealant) [XTC 3D](https://www.smooth-on.com/products/xtc-3d/)
+* XTC 3D Resin Coating for 3D prints (sealant), [XTC 3D](https://www.smooth-on.com/products/xtc-3d/)
 
 ## Existing Ventilator Filters (not N95 compliant)