I keep an excel spreadsheet of my "inventory" of guns, scopes, serial numbers, ammunition, reloading supplies, etc. I update it periodically, bi-annually usually.
I know how much all of the items cost me to purchase and for most, the current selling price is easily determined through Mid South, Midway, Gallery of Guns, or other on-line resource.
The most trouble I have is setting a "current value" of non-warranteed, actively used, out of manufacture scopes (i.e. Redfield 4X Wide Angle gloss blue, Redfield Lo-Pro 3X9 Wide Angle gloss blue, and Bausch & Lomb 3X9 gloss blue) that were purchased with a rifle (B&L), or given as gifts (RFs). Never look a gift horse in the mouth.
These scopes have been trusted friends and hunting companions over decades for me and now my sons. They are neither new nor are they abused. They carry the dings, nicks, and scars of everyday use. Like the trusted companions they are, they work and work well.
I am not interested in selling...just insuring their current values. Any assistance would be appreciated.